Showing papers in "Journal of Fish Biology in 2002"
TL;DR: There is increasing public, governmental and commercial interest in the welfare of intensively farmed fish and stocking density has been highlighted as an area of particular concern, and there are contradictory recommendations in the literature for key water quality parameters to ensure adequate welfare status.
Abstract: There is increasing public, governmental and commercial interest in the welfare of intensively farmed fish and stocking density has been highlighted as an area of particular concern. Here we draw scientific attention and debate to this emerging research field by reviewing the evidence for effects of density on rainbow trout. Although no explicit reference to ‘welfare’ has been made, there are 43 studies which have examined the effects of density on production and physiological parameters of rainbow trout. Increasing stocking density does not appear to cause prolonged crowding stress in rainbow trout. However, commonly reported effects of increasing density are reductions in food conversion efficiency, nutritional condition and growth, and an increase in fin erosion. Such changes are indicative of a reduced welfare status—although the magnitude of the effects has tended to be dependent upon study-specific conditions. Systematic observations on large scale commercial farms are therefore required, rather than extrapolation of these mainly small-scale experimental findings. There is dispute as to the cause of the observed effects of increasing density, with water quality deterioration and/or an increase in aggressive behaviour being variously proposed. Both causes can theoretically generate the observed effects of increasing density, and the relative contribution of the two causes may depend upon the specific conditions. However, documentation of the relationship between density and the effects of aggressive behaviour at relevant commercial densities is lacking. Consequently only inferential evidence exists that aggressive behaviour generates the observed effects of increasing density, whereas there is direct experimental evidence that water quality degradation is responsible. Nevertheless, there are contradictory recommendations in the literature for key water quality parameters to ensure adequate welfare status. The potential for welfare to be detrimentally affected by non-aggressive behavioural interactions (abrasion, collision, obstruction) and low densities (due to excessive aggressive behaviour and a poor feeding response) have been largely overlooked. Legislation directly limiting stocking density is likely to be unworkable, and a more practical option might be to prescribe acceptable levels of water quality, health, nutritional condition and behavioural indicators.
603 citations
TL;DR: This review examines the rationale and value of selecting fishes as bio-indicators of human induced changes within estuaries, using examples from both the northern and southern hemispheres.
Abstract: Estuarine habitats, and the fish assemblages associated with them, are potentially impacted upon by many anthropogenic influences which can have a direct influence on the food resources, distribution, diversity, breeding, abundance, growth, survival and behaviour of both resident and migrant fish species. The direct and indirect coupling between ichthyofaunal communities and human impacts on estuaries reinforces the choice of this taxonomic group as a biological indicator that can assist in the formulation of environmental and ecological quality objectives, and in the setting of environmental and ecological quality standards for these systems. This review examines the rationale and value of selecting fishes as bio-indicators of human induced changes within estuaries, using examples from both the northern and southern hemispheres. The monitoring of estuarine ' health ' using fish studies at the individual and community level is discussed, with an emphasis on the potential use of estuarine fishes and their monitoring and surveillance in national and international management programmes. In illustrating the above concept, examples are presented of the way in which fishes are threatened by anthropogenic impacts and of the way in which teleosts can contribute to a monitoring of estuarine ecosystem health.
462 citations
TL;DR: The need is identified for a well structured experimental approach to the investment of the causes and consequences of hierarchies if the ecology of wild fish is to be modelled eectively based on physiological processes and it is suggested that the further development and application of techniques for monitoring physiologies of fish in the wild is important.
Abstract: Studies of fish behaviour have demonstrated the existence of social interactions that result in dominance hierarchies. In environments in which resources, such as food, shelter and mates, are limited, social competition results in some fish becoming dominant and occupying the most profitable positions. This behaviour has been observed in natural environments and also in many laboratory-based experiments. When two fish have been confined in a small tank, one of them usually has exhibited behaviour that suggests it is dominant over the other submissive animal. Physiological consequences of social interaction can be seen in both dominants and subordinates but are more extreme in the subordinate. However, this scenario is without doubt an artificial situation. Fewer experiments have been conducted using laboratory experiments that are more socially and physically complex than those experienced by dyads in tanks. In simple fluvial tanks, through which water is recirculated, the physiological responses of fish to social competition have generally been qualitatively similar to those recorded among dyads. However, when environmental disturbances, complex resource distributions, increase in water flushing, presence of predators and competing species of fish have been included in experimen-tal designs, there have been fewer, diminished or no physiological dierences between dominant and subordinate fish. There have been very few studies of physiology in relation to dominance in natural habitats, and those that have been conducted suggest that under some circumstances hierarchies may cause less intense physiological responses than have been suggested based on results of laboratory studies in simple environments. Possible reasons for these variations are discussed. The need is identified for a well structured experimental approach to the investi-gation of the causes and consequences of hierarchies if the ecology of wild fish is to be modelled eectively based on physiological processes. It is also suggested that the further development and application of techniques for monitoring physiologies of fish in the wild is important.
231 citations
TL;DR: Response curves developed for induction and recovery time considered the following predictors: clove oil concentration, sex, fish length and depth, and a significant positive dependence was observed between induction time and fish length for 20, 50 and 80 mg 1−1 test concentrations.
Abstract: Wild migrating sockeye salmon Oncorhynchus nerka exposed to 20, 50 and 80 mg 1−1 of clove oil could be handled within 3 min, recovered within 10 min, and survived 15 min exposure trials. Fish tested at 110 mg 1−1 did not recover from 15 min exposure trials. Response curves developed for induction and recovery time considered the following predictors: clove oil concentration, sex, fish length and depth. A significant positive dependence was observed between induction time and fish length for 20, 50 and 80 mg 1−1 test concentrations; no dependence was observed between induction time and length at 110 and 140 mg 1−1. Recovery time differed as a function of clove oil concentration, but not fish size. A concentration of 50 mg 1−1 is recommended for anaesthetizing sockeye salmon ranging in length from 400 to 550 mm at water temperatures averaging 9–10° C.
204 citations
TL;DR: In 36 south Finnish lakes, the number of species, as well as the cyprinids:percids ratio, was dependent, not only on total phosphorus (TP), but also on lake size.
Abstract: In 36 south Finnish lakes, the number of species, as well as the cyprinids:percids ratio, was dependent, not only on total phosphorus (TP), but also on lake size. Total fish biomass and cyprinid biomass increased along the TP gradient, whereas the dependence of percid biomass was less evident. Perch Perca fluviatilis and roach Rutilus rutilus strongly dominated mesotrophic lakes; in eutrophic lakes the proportion of other cyprinids and percids, such as white bream Blicca bjoerkna, bream Abramis brama, pikeperch Stizostedion lucioperca and ruffe Gymnocephalus cernuus, increased. Perch biomass was weakly related to abiotic factors but depended on roach biomass. Lake size and fish species composition are essential factors affecting fish community changes in relation to TP, and may be important as well in regulating the responses of a fish community to biomanipulation.
184 citations
TL;DR: It is demonstrated that the morphological variation in caudal area exhibited by wild juvenile brook charr from microhabitats differing in water velocity could be a consequence of phenotypic plasticity in response to hydrological conditions.
Abstract: In the field, juvenile brook charr Salvelinus fontinalis inhabiting high-velocity water were found to have larger caudal fins and more slender bodies than those inhabiting low-velocity water. Young-of-the-year S. fontinalis were reared in either a high- or low-velocity treatment for 16 weeks and their morphology was measured bi-weekly. From the second to fourth weeks of the experiment onwards, fish reared in the high-velocity treatment had larger maximum caudal fin heights and deeper caudal peduncles than fish reared in the low-velocity treatment. This study demonstrated that the morphological variation in caudal area exhibited by wild juvenile brook charr from microhabitats differing in water velocity could be a consequence of phenotypic plasticity in response to hydrological conditions.
180 citations
TL;DR: Stereological estimation indicated that the ovaries of spawning bluefin tuna from the Balearic Islands contained five-fold more highly yolked oocytes than bluefin fish from Barbate, indicating that the gonad is at an incipient stage of maturation.
Abstract: The ovarian mass and gonadosomatic index (IG) of bluefin tuna Thunnus thynnus, caught in the Strait of Gibraltar (Barbate) during migration to Mediterranean spawning grounds, were several times lower than those found in bluefin tuna from Mediterranean spawning grounds (Balearic Islands). Some of the bluefin tuna from Barbate (8.3%) were classified as immature (the most advanced oocytes present in the ovaries were early vitellogenic), and the majority (the remaining 91.6%) as non-spawning mature; the ovary contained late vitellogenic oocytes, but there was no sign of spawning activity. Stereological estimation indicated that the ovaries of spawning bluefin tuna from the Balearic Islands contained five-fold more highly yolked oocytes than bluefin tuna from Barbate. When breeding bluefin tuna cross the Strait of Gibraltar the gonad is at an incipient stage of maturation. The average batch fecundity estimated from stereological quantification of stage 4 (migratory-nucleus) oocytes in the specimens collected from Balearic was 92.8 oocytes g-1‘of body mass, and the spawning frequency in this area was calculated to be 1.2 days. In specimens from Barbate a relative batch fecundity of 96.3 oocytes g -1 was estimated using stage 3 (late vitellogenic) oocyte counts.
141 citations
TL;DR: A single-sex model is presented that calculates the probability of detecting multiple mating (PrDM) given genetic data from the single genetic parent and a sample of its offspring and the effects of numbers of loci, alleles, offspring and genetic parents contributing to the multiple mating.
Abstract: A single-sex model is presented that calculates the probability of detecting multiple mating (PrDM) given genetic data from the single genetic parent and a sample of its offspring. The model incorporates the effects of numbers of loci, alleles, offspring and genetic parents contributing to the multiple mating, all of which effect PrDM. The model is used to determine the actual number of loci and offspring that are required to detect multiply mated broods with high probability (80 and 95%). For example, if two sires contribute with equal fertilization success to multiply mated broods, then only 10 offspring and one locus with seven equally common alleles are required to ensure that 80% of multiple mated broods are detected. Ninety-five per cent of multiple mated broods can be detected with 10 offspring and five loci with four equally common alleles. The utility of the model is demonstrated with biological examples addressing geographic variation in multiple paternity among natural populations of guppies Poecilia reticulata and mosquitofish Gambusia holbrooki.
139 citations
TL;DR: Overall, there was good agreement between gut content and stable isotope data indicating that the latter may be useful as a tool in trophic studies in marine protected areas where sampling for fishes is not allowed.
Abstract: The diet of the dusky grouper Epinephelus marginatus, from the Balearic Islands, western Mediterranean, consisted primarily of crustaceans, molluscs and fishes, but diet composition varied with body size. The smaller dusky groupers (<300 mm L T ) fed primarily on crustaceans, and particularly on brachyurans, which accounted for 46% of the prey identified. As dusky groupers grew, cephalopods became increasingly important and constituted 10 to 40% of the prey identified in subadult and adult specimens. The largest dusky groupers fed primarily on fishes that represented 40.9% of prey identified. These shifts in diet were accompanied by a positive selection of increasingly large prey and by an expansion of trophic niche. δ 15 N values of dusky grouper white muscle ranged from 8.8 to 13.1‰ and 71% of the variation in δ 15 N was explained by differences in dusky grouper size. δ 13 C values ranged from - 17.9 to - 15.9‰, and no significant body size effect on δ 13 C was detected. Stomach content and 13 C values indicated that from 1 year old, the diet of E. marginatus was based on the benthic food web. The enrichment in δ 15 N registered from juvenile to large males was c. 3.8‰. Overall, there was good agreement between gut content and stable isotope data indicating that the latter may be useful as a tool in trophic studies in marine protected areas where sampling for fishes is not allowed.
138 citations
TL;DR: The knife-edge response in school behaviour suggests that the relative abundance of determined individuals in a school plays an important part in the collective behaviour.
Abstract: According to the adopted-migrant hypothesis, first time spawning herring Clupea harengus learn their migration pattern from schooling with older individuals. Changes in migration pattern of Norwegian spring-spawning herring co-occur with the recruitment of abundant year classes to the spawning stock. It is argued that this is due to the abundant year classes being unable to learn from the older ones since most of the recruiting year class only experience their own naive class-mates. An individual-based school simulation study is presented to explore the hypothesis. Behaviour is simulated using individual rules that take into account the movements of nearby individuals. After establishing a schooling pattern, a small proportion of the individuals is directed to move towards a given position while the remaining individuals keep using their behaviour rules. When <4% of the individuals are so directed there is no response seen in the remaining school. But when ≥7% of the total school is directed to a specific location, the remaining individuals always respond and follow the directed individuals. The simulations thus show that determined individuals can have a substantial influence on the collective behaviour of schools. Furthermore, the knife-edge response in school behaviour suggests that the relative abundance of determined individuals in a school plays an important part in the collective behaviour. This mechanism can explain the observed changes in migration pattern of Norwegian spring-spawning herring associated with the recruitment of abundant year classes to the adult stock.
136 citations
TL;DR: While hydrodynamic factors appear to be very important to larval fish swimming performance in cold water, they appear to lose importance in warm water where temperature effects on physiology dominate, which may suggest that major differences exist among locomotory capacities of larvalFish that inhabit cold, temperate waters compared to those that live in warm tropical waters.
Abstract: Temperature influences both the physiology offish larvae and the physics of the flow conditions under which they swim. For small larvae in low Reynolds number (Re) hydrodynamic environments dominated by frictional drag, temperature-induced changes in the physics of water flow have the greatest effect on swimming performance. For larger larvae, in higher Re environments, temperature-induced changes in physiology become more important as larvae swim faster and changes in swimming patterns and mechanics occur. Physiological rates at different temperatures have been quantified using Q10s with the assumption that temperature only affected physiological variables. Consequently, Q10s that did not consider temperature-induced changes in viscosity overestimated the effect of temperature on physiology by 58% and 56% in cold-water herring and cod larvae respectively. In contrast, in warm-water Danube bleak larvae, Q10s overestimated temperature-induced effects on physiology by only 5–7%. This may be because in warm water, temperature-induced changes affect viscosity to a smaller degree than in cold water. Temperature also affects muscle contractility and efficiency and at high swimming velocities, efficiency decreases more rapidly in cold-exposed than in warm-exposed muscle fibres. Further experiments are needed to determine whether temperature acts differently on swimming metabolism in different thermal environments. While hydrodynamic factors appear to be very important to larval fish swimming performance in cold water, they appear to lose importance in warm water where temperature effects on physiology dominate. This may suggest that major differences exist among locomotory capacities of larval fish that inhabit cold, temperate waters compared to those that live in warm tropical waters. It is possible that fish larvae may have developed strategies that affect dispersal and recruitment in different aquatic habitats in order to cope not only with temperature-induced physiological challenges, but physical challenges as well.
TL;DR: The results suggest that in some species, smaller fins may be favoured in stream-dwelling individuals because the reduction of drag during swimming more than compensates for their reduced power and propulsion efficiency in a current.
Abstract: Pumpkinseed Lepomis gibbosus and rock bass Ambloplites rupestris stream populations of both sexes were significantly different in external morphology from lake populations in a central Ontario, Canada, watershed. The predictions that stream fishes would be more slender-bodied, and have a more anterior placement of lateral fins than lake fishes were generally supported. The prediction that stream fishes would have a more robust caudal peduncle was partially supported. The prediction that fin size would be larger in stream fishes was not supported, as lake rock bass generally had longer and wider fins than those from stream sites. The results suggest that in some species, smaller fins may be favoured in stream-dwelling individuals because the reduction of drag during swimming more than compensates for their reduced power and propulsion efficiency in a current. Smaller fin size in stream-dwelling centrarchids may be related to their body shape, or to their low usage of fast-moving water within the streams they inhabit.
TL;DR: Only in tropical estuaries are animals from such a wide range of taxa so closely associated, annelid worms, prawns, crocodiles, birds, 'hippos', dolphins and of course fishes, all may form part of the overall community, often with functional ecological links.
Abstract: Tropical estuarine areas comprise small systems of a few km, larger estuaries, coastal lakes of hundreds of km 2 and vast shallow coastal waters that are contiguous with estuaries and have similar reduced salinities. Many of the world's great estuaries are in the tropics, e.g. the Amazon, Orinoco, Congo, Zambezi, Niger, Ganges and Mekong. The distribution of tropical and subtropical estuaries approximately follows that of mangroves. Like estuaries everywhere, they are a focus of human activity and are among the most exploited of ecosystems. In few other places do the activities of fishers, industrialists, shippers, farmers, conservationists, sports enthusiasts and biologists overlap to such an extent. Quite apart from the possible effects of all these activities, the fishes of subtropical and tropical estuaries already face one of the most rigorous of aquatic environments; but despite this, species diversity and productivity are high. Only in tropical estuaries are animals from such a wide range of taxa so closely associated, annelid worms, prawns, crocodiles, birds, 'hippos', dolphins and of course fishes, all may form part of the overall community, often with functional ecological links. Unfortunately, the difficulties of working in these often inhospitable environments, has meant that biologists have favoured projects in more appealing areas, such as coral reefs. While it is still true that most estuarine research is conducted in industrialized developed countries, nearly all of which are in cold or temperate regions, there has been a recent upsurge in tropical estuarine fish research. This is being driven by two imperatives, food security and the conservation and maintenance of biodiversity. Both these problems require knowledge of the ecology of tropical estuarine fishes, particularly their relationships with the environment and the extent to which they are dependent on estuaries or adjacent habitats for survival.
TL;DR: Changes in alkali-labile phosphorous, a specific biomarker of exposure to estrogenic contaminants, can be detected in whole-body preparations of estrogen-exposed sticklebacks confirming that the measurement of biomarkers normally assessed in a specific tissue can be equally possible in whole fish.
Abstract: Indicators of a generalised stress response (changes in cortisol, glucose, RNA:DNA ratio and total protein) when measured in whole-body preparations of individual sticklebacks display significant alterations in response to acute (hours) and chronic (days) disturbances and food withdrawal. In addition, changes in alkali-labile phosphorous, a specific biomarker of exposure to estrogenic contaminants, can be detected in whole-body preparations of estrogen-exposed sticklebacks confirming that the measurement of biomarkers normally assessed in a specific tissue can be equally possible in whole fish.
TL;DR: Ovarian fluid enhances sperm movement in Arctic charr Sahelinus alpinus sperm and thus has the potential to influence both fertilization success and the outcome of sperm competition.
Abstract: Like the spermatozoa of most other fish species spawning in fresh water, Arctic charr Sahelinus alpinus sperm were short-lived (mean 42 s) after activation and their swimming speed declined rapidly during this period, e.g. from a mean speed of 106 um s−1 at 10 s after activation in fresh water to 21 μm s−1 only 20 s later. Ovarian fluid significantly influenced sperm longevity (duration of forward mobility), per cent motility, swimming speed and the linearity of sperm movement. All of these variables generally increased as the concentration of ovarian fluid increased from 0 to 50%, even though ovarian fluid is more than three times as viscous as fresh water. It is concluded that ovarian fluid enhances sperm movement in this species and thus has the potential to influence both fertilization success and the outcome of sperm competition.
TL;DR: In aquaria, adults and young-of-the-year (YOY) of both Spanish toothcarp Aphanius iberus and Valencia hispanica received more aggression in the presence of eastern mosquitofish Gambusia holbrooki, and aggression almost disappeared at low water temperatures.
Abstract: In aquaria, adults and young-of-the-year (YOY) of both Spanish toothcarp Aphanius iberus and Valencia toothcarp Valencia hispanica received more aggression in the presence of eastern mosquitofish Gambusia holbrooki. YOY of both species also showed decreased feeding rates, as did V. hispanica adults. Adult V. hispanica also were more aggressive themselves and had their reproductive behaviour disrupted. Cases of eastern mosquitofish predation on small A. iberus were also observed. The occurrence and intensity of these potentially harmful effects, however, seemed to be modulated by water temperature, reproductive condition, relative size of the interacting fishes and species-specific habitat preferences. Thus, aggression almost disappeared at low water temperatures. Valencia hispanica and eastern mosquitofish used similar vertical positions in the water column and this apparently increased the frequency of their interactions. In contrast, A. iberus preferred positions closer to the bottom than the other two species and this vertical segregation appeared to lead to less direct interaction with eastern mosquitofish. In an outdoor mesocosm experiment, under semi-natural conditions, the presence of eastern mosquitofish resulted in an almost 70% reduction in the number of o.spring produced by A. iberus. The addition of extra, non-breeding males of A. iberus had no significant effect. YOY A. iberus from cages with eastern mosquitofish or extra males were significantly smaller (c. 1 mm, or 8% shorter) than those from cages without additional fish. Results for V. hispanica were not conclusive, as very few YOY were recovered. In contrast, eastern mosquitofish did not affect the survivorship of breeding adults of both native species.
TL;DR: It is suggested that egg surface and adhesiveness may be related to reproductive patterns and to phylogenesis.
Abstract: Eggs of 23 Characiformes and eight Siluriformes, belonging to nine families with diverse reproductive behaviour, were ultrastructurally analysed. The migratory species exhibited non-adhesive eggs, whereas, most of the sedentary species presented some degree of egg adhesiveness. Among the Characiformes, non-adhesive eggs showed zona radiata with pore-canals or a fibrillar net at the surface; weakly adhesive eggs presented only zona radiata with pore-canals while adhesive eggs exhibited zona radiata with apparatus like globules, filaments, villi or honeycomb-like pores depending on the systematic group. The ‘jelly’ coat is strongly related to the Siluriformes eggs apparently without relationship with adhesiveness. A micropylar disc was present in adhesive eggs of a few species of both Characiformes and Siluriformes. Some patterns were characteristic of the animal pole, others of the vegetal pole, and others were common to both poles. The radial ridges converging to the micropyle in Astyanax bimaculatus lacustris appear to be related to fertilization. In general, egg surface structures in the Characiformes varied according to the genus, whereas all Siluriformes showed a similar egg surface pattern, regardless of the group analysed. Multivariate analysis allowed the identification of eight clusters among the Characiformes and three among the Siluriformes showing relationships between reproductive style and egg characteristics. It is suggested that egg surface and adhesiveness may be related to reproductive patterns and to phylogenesis.
TL;DR: Morphological development, allometric growth and behaviour of hatchery-reared California halibut Paralichthys californicus were studied from hatching to metamorphosis.
Abstract: Morphological development, allometric growth and behaviour of hatchery-reared California halibut Paralichthys californicus were studied from hatching to metamorphosis (42 days post hatch, dph) at 187° C. Mean standard length (LS) of larvae and juveniles increased from 2.1 mm at hatching to 10.5 mm at metamorphosis with the increase in length being approximately linear. Stages of morphological development were described using the alphabetic staging (A–I) used for other flatfish species. Organogenesis and differentiation were more rapid and complex in yolk-sac (hatching, stage A–3 dph, stage B), preflexion (3–19 dph, stages B–C), and flexion larvae (from 20 to 23 dph, stages D–E), as larvae developed most of their sensory, feeding, respiratory and swimming systems. After notochord flexion at 24–25 dph (stage F), most morphological changes were related to the progressive transformation from a bilateral symmetrical larva to an asymmetrical benthic juvenile (42 dph, stages G–I).
TL;DR: Based on 16 months of field observations on tagged seahorses Hippocampus comes in the Philippines, adults were found to be nocturnal, to maintain small home ranges, and to live mostly among corals, a conclusion consistent with their low density and sparse distribution.
Abstract: Based on 16 months of field observations on tagged seahorses Hippocampus comes in the Philippines, adults were found to be nocturnal, to maintain small home ranges, and to live mostly among corals. Prolonged pair associations suggested that H. comes, like many other seahorse species, were probably monogamous, a conclusion consistent with their low density and sparse distribution. Site and mate fidelity suggest that H. comes populations may fare poorly under current high levels of exploitation.
TL;DR: The large changes in consumption of euphausiids and Atlantic herring represent highly significant changes and would need to be included in the development and interpretation of ecosystem-based management models for this ecosystem.
Abstract: Major temporal changes in the importance of euphausiids and Atlantic herring Clupea harengus in the diet of Atlantic cod Gadus morhua, 10-75 cm L F , occurred in shallow waters ( 45 cm L F ) largely replaced euphausiids in the Atlantic cod diets from 1990 to 2000. This diet change suggested there has been a major perturbation of the food web of the southern Gulf of St Lawrence. The importance of fishes (mostly Atlantic herring) in the diet of Atlantic cod >45 cm L F increased significantly between the periods 1959-1980 and 1987-2000. Atlantic herring comprised 0-4% (mean 1.3%) of prey mass of Atlantic cod 46-60 cm L F from 1959 to 1980 and increased to 2-42% (mean 19.6%) of the diet from 1987 to 2000. Atlantic herring comprised 0-25% (mean 9.4%) of the prey mass of Atlantic cod 61-75 cm L F from 1959 to 1980 and increased to 42-81% (mean 542%) of prey mass from 1987 to 2000. This increased consumption of Atlantic herring was consistent with observed changes in abundance of Atlantic herring in the ecosystem between the late 1970s and 2000. The large changes in consumption of euphausiids and Atlantic herring represent highly significant changes and would need to be included in the development and interpretation of ecosystem-based management models for this ecosystem.
TL;DR: The seasonal coincidence of maximal fish and key-prey species densities suggests that food availability may be a principal factor influencing the nursery function of the Guadalquivir Estuary.
Abstract: In the analysis of the feeding habits of the 11 most abundant fish species in the Guadalquivir Estuary, collected monthly (February 1998 to January 1999) at two different sampling sites, a total of 46 prey taxa were identified. Classifications (based on Bray-Curtis similarities derived from occurrence, number and mass data) of the different fish categories (postlarvae and juvenile--adults of each species) revealed two main trophic guilds, whose preferential prey (SIMPER analysis) were mysids and copepods, respectively. The similarity matrices derived from occurrence, number and mass data were always significantly correlated (RELATE: r>0.636; P<0.01), indicating that a good agreement in feeding patterns emerged from these variables. The seasonal coincidence of maximal fish and key-prey species densities suggests that food availability may be a principal factor influencing the nursery function of the Guadalquivir Estuary.
TL;DR: The morphological organization of the male brood pouch skin of three different species of syngnathids, investigated using light and electron microscopy, showed that each pouch had a skin with a different ultrastructure, which reflected different relationships between the paternal body and the developing embryos.
Abstract: The morphological organization of the male brood pouch skin of three different species of syngnathids (Nerophis ophidion, Syngnathus abaster and Hippocampus hippocampus), investigated using light and electron microscopy, showed that each pouch had a skin with a different ultrastructure. This reflected different relationships between the paternal body and the developing embryos. In N. ophidion, the bilayered epidermis of the pouch consisted mainly of pavement cells (filament-containing cells) typical of fish skin. In S. abaster, pavement cells were interspersed with many mitochondria-rich cells. These cells varied in number during the different functional stages of the pouch and died by apoptosis after the breeding period. Modified secretory ‘flame cone cells’ rich in vesicles and granules characterized the epidermis of H. hippocampus. Although there were specific differences, the vascularized dermis was the only feature common to all three types of pouch. These findings suggest that the brood pouch in Syngnathidae has different functions, which may be related to the different reproductive strategies and ecology of each species.
TL;DR: Radio-tagged smolts of Atlantic salmon and sea trout were predated heavily by sea birds after crossing the saline limit in the estuary of the River Skjern, Denmark, but the field data do not contradict the hypothesis of maladaptive anti-predatory behaviour.
Abstract: Radio-tagged smolts of Atlantic salmon Salmo salar and sea trout Salmo trutta were predated heavily by sea birds after crossing the saline limit in the estuary of the River Skjern, Denmark. Most predation took place within the first 9 h after estuarine entry. The field data do not contradict the hypothesis of maladaptive anti-predatory behaviour.
TL;DR: There were significant negative associations, however, between sperm total and flagellum length and ejaculate longevity, so that males with longer sperm had shorter-lived gametes, supporting the theory that increased hydrostatic forces generated by longer flagella may trade against sperm cell longevity.
Abstract: Relationships between spermatozoal design and swimming behaviour were investigated using the significant natural variance in sperm traits in Atlantic salmon Salmo salar. In vitro motility and fertilization experiments were conducted with 86 Atlantic salmon to measure sperm form and function under natural fertilization conditions. Spermatozoal traits of Atlantic salmon showed narrow variance within individuals but differed extensively between samples: mean sperm length varied from 32.3 to 39.5 μm, mean velocity ranged from 18 to 127 μm s -1 , and ejaculate longevity varied from 18 to 78 s. In addition to variation in sperm morphometry between fish, a negative relationship was also found between sperm head length and flagellum length. This natural variation in sperm form and function between males is counter-intuitive since measures are from a single Atlantic salmon population where all males are adapted to a common fertilization environment. No evidence was found that longer sperm, or sperm with longer flagella, achieved faster swimming velocities. Also no evidence was found for a trade-off between mean sperm velocity and ejaculate longevity. There were significant negative associations, however, between sperm total and flagellum length and ejaculate longevity, so that males with longer sperm had shorter-lived gametes. This finding has previously been reported in a study across fish species, supporting the theory that increased hydrostatic forces generated by longer flagella may trade against sperm cell longevity.
TL;DR: It is concluded that the fish assemblage in rocky habitats is dominated by permanent non-commercial species, whereas soft bottoms mainly function as nurseries for juvenile fishes and as feeding grounds for seasonal migrants of commercial species.
Abstract: Density and biomass of fishes, from shallow rocky and soft bottom habitats on the Swedish west coast, showed large seasonal variation with low values in winter and spring and with peaks in June Season was also the most important factor determining the fish assemblage structure Within season, however, there was a clear separation in assemblage structure between rocky-and soft-bottom habitats There were significantly higher total fish abundances and biomasses during night compared with day catches On soft bottoms density and biomass of fishes decreased with increasing depth, but no such pattern was seen in rocky habitats indicating that the distribution of fishes was related to vegetation cover Altogether, 53 fish species were recorded of which 30 were common to both habitats Species richness was similar on rocky and soft bottoms Of the 10 most abundant species found in rocky habitats four belonged to the Labridae and three to the Gadidae The fish assemblage on soft bottoms were of a more mixed nature with representatives among the 10 dominants from six families (Clupeidae, Cottidae, Gadidae, Gobiidae, Labridae and Pleuronectidae) When ranking the 10 dominant fish species on rocky bottoms according to biomass c 50% of the mass was Labridae, 19% Gadidae and 13% Cottidae In soft bottom habitats, fish biomass was mainly distributed between six families Pleuronectidae and Gadidae were dominant and each made up 25% of the biomass, whereas Labridae only contributed 4% of the fish mass It is concluded that the fish assemblage in rocky habitats is dominated by permanent non-commercial species (63% of biomass), whereas soft bottoms mainly function as nurseries for juvenile fishes and as feeding grounds for seasonal migrants of commercial species (80% of biomass)
TL;DR: Isotope and stomach content analyses yielded consistent results and indicated short- and long-term reliance on fish as a food for large Arctic charr and the observed cannibalism by large-form individuals does not act to maintain the bimodal length-frequency distribution in Lake Hazen.
Abstract: Stable isotopes of carbon and nitrogen were used to examine differences in the feeding ecology of sympatric morphotypes of Arctic charr Sahelinus alpinus from Lake Hazen, Ellesmere Island, in the Canadian High Arctic. Large and small morphotypes possessed significantly different carbon and nitrogen signatures with large-form Arctic charr being more depleted in 13C and more enriched in 15N than the small-form. Isotope and stomach content analyses yielded consistent results and indicated short- and long-term reliance on fish as a food for large Arctic charr. Large-form individuals predate on juveniles but do not predate on small-form individuals ≥ 250 mm. The observed cannibalism by large-form individuals, therefore, does not act to maintain the bimodal length-frequency distribution in Lake Hazen. Bimodality is argued to arise for ecological reasons connected with differing habitat use by the morphotypes and the associated differences in resource consumption opportunities.
TL;DR: Trairas can survive food deprivation for periods of up to 180 days without reductions in metabolism and when they do become hypometabolic, normal metabolic rates are rapidly restored upon refeeding, contributing to energy conservation during these periods of starvation.
Abstract: Growth of adult trairas Hoplias malabaricus ceased and body mass (M) decreased during starvation periods of 30, 60, 90, 150, 180 and 240 days. Hepatic reserves were mobilized in fish starved for 30 days, but liver mass of fish starved for longer periods was not significantly different from those starved for 30 days. Perivisceral fat bodies were consumed gradually, being completely exhausted after 240 days of food deprivation. Length of starvation was associated with a significant decrease in the oxygen uptake (VO 2 ). In spite of this reduction, the respiratory frequency (f R ) was kept nearly constant during the starvation periods. The haematocrit and the number of red blood cells decreased after 150 and 240 days of starvation, respectively. These parameters did not recover after refeeding (after 90 and 240 days of starvation). This hypometabolic state in response to food deprivation contributed to energy conservation during these periods. Trairas can survive food deprivation for periods of up to 180 days without reductions in metabolism and when they do become hypometabolic, normal metabolic rates are rapidly restored upon refeeding.
TL;DR: Established populations of P. parva have now been found in the wild, in large numbers, at several locations across England.
Abstract: Pseudorasbora parva has demonstrated, in less than four decades, its invasive potential by colonizing much of continental Europe. Established populations of P. parva have now been found in the wild, in large numbers, at several locations across England. At present, only one deliberate introduction is known to have taken place during the mid-1980s at Crampmoor Fisheries, Hampshire.
TL;DR: The species composition and dynamics of fish larvae in three mangrove creeks located in the Caete Estuary (north Brazil) were studied monthly using a trap net during diurnal ebb tides, indicating continuous transport out of the mangroves by tidal currents.
Abstract: The species composition and dynamics of fish larvae in three mangrove creeks located in the Caete Estuary (north Brazil) were studied monthly using a trap net during diurnal ebb tides. A total of 109 954 larvae, representing 25 families and 54 species, were collected from October 1996 to October 1997. The community was dominated numerically by a few species, a feature common for other estuarine fish populations. The most abundant taxa were estuarine species, namely the eleotrid Guavina guavina (46.7%) and the engraulid Anchovia clupeoides (14.9%). The sciaenid Cynoscion acoupa was the only marine species that used the mangroves extensively as a nursery site, occurring mainly at the postflexion stage. The size distribution of G. guavina did not produce shifting modes, indicating continuous transport out of the mangroves by tidal currents. Significantly lower species richness was observed in the late rainy season, primarily due to the emigration of marine species. Intermediate seasons were characterized by more complex larval fish assemblages. The temporal trends of the dominant species was influenced to a great degree by their life history strategy.
TL;DR: There were differences in parasite diversity and intensity of infection among river compared to lake populations suggesting a role for parasites as selective agents in the ecological divergence of three-spined sticklebacks.
Abstract: Two ciliates and 16 metazoan parasites were identified in 434 0+ year three-spined sticklebacks Gasterosteus aculeatus collected from two small rivers and four lakes located in Schleswig-Holstein, Germany. By repeated sampling and analysis of dispersion patterns of six frequently occurring parasites no consistent evidence was found for mortality induced by a single parasite species. Linear log-variance to log-mean abundance ratios with slopes of c. 2 indicated negative binomial distributions for five of the six parasites. The numbers of these six parasites were combined as multiples of S.D. of each parasite species over all samples to form an ‘individual parasitation index’ (IPI), which showed that only in one locality a slight decrease in parasite burden occurred between September and April. In two of the lake populations, however, there was a distinct decline in the degree of dispersion in spring samples. This indicates that a combination of different species might cause parasite-induced host mortality, undetectable by patterns obtained from single species. There were differences in parasite diversity and intensity of infection among river compared to lake populations suggesting a role for parasites as selective agents in the ecological divergence of three-spined sticklebacks.