Showing papers in "Journal of Fish Biology in 2001"

Accuracy, precision and quality control in age determination, including a review of the use and abuse of age validation methods

Abstract: Many calcified structures produce periodic growth increments useful for age determination at the annual or daily scale. However, age determination is invariably accompanied by various sources of error, some of which can have a serious effect on age-structured calculations. This review highlights the best available methods for insuring ageing accuracy and quantifying ageing precision, whether in support of large-scale production ageing or a small-scale research project. Included in this review is a critical overview of methods used to initiate and pursue an accurate and controlled ageing program, including (but not limited to) validation of an ageing method. The distinction between validation of absolute age and increment periodicity is emphasized, as is the importance of determining the age of first increment formation. Based on an analysis of 372 papers reporting age validation since 1983, considerable progress has been made in age validation efforts in recent years. Nevertheless, several of the age validation methods which have been used routinely are of dubious value, particularly marginal increment analysis. The two major measures of precision, average percent error and coefficient of variation, are shown to be functionally equivalent, and a conversion factor relating the two is presented. Through use of quality control monitoring, ageing errors are readily detected and quantified; reference collections are the key to both quality control and reduction of costs. Although some level of random ageing error is unavoidable, such error can often be corrected after the fact using statistical (‘digital sharpening)’ methods.

Social learning and life skills training for hatchery reared fish

Abstract: With the stress placed on our natural resources, many fisheries increasingly rely on restocking from hatchery-reared sources in an attempt to maintain commercially viable populations. However, the mortality rates of hatchery-reared fishes during the period directly following release are very high. The successful development of restocking programs is consequently dependent upon production and release strategies that lead to improved migratory, antipredator and feeding behaviour in hatchery fish. While relevant individual experience prior to release might improve performance, social learning potentially provides a process whereby fish can acquire locally adaptive behaviour rapidly and efficiently. It is now well over a decade since Suboski & Templeton (1989) raised the possibility of using social learning processes to improve the post-release survival of hatchery-reared fishes. This period has witnessed considerable progress in the understanding of how social learning operates in fish populations. We review new methods and recent findings that suggest how social learning protocols could realistically be applied on a large scale to enhance the viability of hatchery fish prior to their release into the wild. We also suggest a practical pre-release training protocol that may be applied at the hatchery level.

Polymorphism and speciation in Arctic charr

Abstract: The Arctic charr Salvelinus alpinus exhibits 1–4 sympatric morphs in postglacial lakes, of which one or two are epibenthic zoobenthos feeders, one is a limnetic planktivore and one is a piscivorous form. In addition, northern rivers support partly migratory populations with anadromous and freshwater resident fish. The morphs vary in their coloration, morphology, life history, behaviour and genetic characteristics. The morphs usually differentiate according to their ontogenetic stage at maturity, which parallels paedomorphism in amphibians. The young usually start as epibenthic zoobenthivores, but may become pelagic at a certain size according to the predation risk experienced at that time. From a length of > 20–25 cm, charr start to become piscivorous. The proportion of piscivorous fish increases with increasing body size. In partly anadromous populations, fish that mature before smolting become freshwater resident, the others anadromous. In some rivers, the morphs occupy separate niches (epibenthic and limnetic), from emergence onwards. The morphs exhibit different degrees of reproductive isolation that vary from a high degree of interbreeding to complete isolation. Usually, they spawn within morph (assortative mating), but alternative male mating behaviour (sneaking, fighting) may occur in stream-spawning populations and at great depths in lakes. Morphologically specialized morphs appear to feed more effectively than intermediate forms, and selection according to feeding mode, site fidelity and associated assortative mating are prerequisites for the evolution of the different morphs. Charr morphs develop into stable feeding niches under conditions of intense intraspecific competition when there is little competition with other species. Sympatric morphs exhibit different degrees of speciation, but similar morphs in different systems are not individual species because of (1) their polyphyletic origin, (2) the supporting systems are often young, transient environments making the future situation for the populations uncertain, and (3) the genetic differentiation among morphs is low. Sympatric morphs may interbreed and produce fertile hybrids. Nevertheless, sympatric charr morphs should be managed as separate species. Changes in the natural conditions or human impacts to which the morphs are adapted will have a strong influence on the persistence and survival of each different morph.

Effects of marine reserve characteristics on the protection of fish populations: a meta‐analysis

Abstract: Meta-analyses of published data for 19 marine reserves reveal that marine protected areas enhance species richness consistently, but their effect on fish abundance is more variable. Overall, there was a slight (11%) but significant increase in fish species number inside marine reserves, with all reserves sharing a common effect. There was a substantial but non-significant increase in overall fish abundance inside marine reserves compared to adjacent, non-reserve areas. When only species that are the target of fisheries were considered, fish abundance was significantly higher (by 28%) within reserve boundaries. Marine reserves vary significantly in the extent and direction of their response. This variability in relative abundance was not attributable to differences in survey methodology among studies, nor correlated with reserve characteristics such as reserve area, years since protection, latitude nor species diversity. The effectiveness of marine reserves in enhancing fish abundance may be largely related to the intensity of exploitation outside reserve boundaries and to the composition of the fish community within boundaries. It is recommended that studies of marine reserve effectiveness should routinely report fishing intensity, effectiveness of enforcement and habitat characteristics.

Freshwater fish introductions in Spain: facts and figures at the beginning of the 21st century

Abstract: Twenty-five introduced fish species are established in Spanish fresh waters. Most of the introductions took place after 1900, with a significant exponential increase during the second half of the 20th century (15 species introduced from 1949). Major stocking efforts in Spanish waters have been suspended, but recently some species have been released by anglers or are suspected to be escapes from fish farms. Stream regulation is considered to be one of the main negative factors affecting river ecosystems in Spain, but many of the aliens adapt well to these altered habitats. Competition between native and exotic fishes is certain to occur to some degree, but there is little quantitative information. Fish conservation and fishery management must not be based on the ‘introduce anything’ sentiment that has developed over more than a century. Information, education and public awareness are critical components of any effort to prevent the spread of introduced fish species.

Visual census methods underestimate density and diversity of cryptic reef fishes

Abstract: The diversity and density of small, benthic reef fishes were estimated using visual census and enclosed rotenone stations. Visual census underestimated the number of species present and the density of common species by up to 91%.

Comparative effects of long‐term hypoxia on growth, feeding and oxygen consumption in juvenile turbot and European sea bass

Abstract: When juvenile turbot Scophthalmus maximus and sea bass Dicentrarchus labrax were fed to satiation, growth and food intake were depressed under hypoxia (3·2±0·3 and 4·5±0·2 mg O2 l -1 ) However, no significant difference in growth was observed between fishes maintained in hypoxia and fed to satiation and fishes reared in normoxia (7·4±0·3 mg O2 l -1 ) and fed restricted rations (same food intake of fishes at 3·2 mg O2 l -1 ) Routine oxygen consumption of fishes fed to satiation was higher in normoxia than in hypoxia due to the decrease in food intake in the latter Of the physiological parameters measured, no significant changes were observed in the two species maintained in hypoxia This study confirms the significant interaction between environmental oxygen concentrations, feeding and growth in fishes Decrease in food intake could be an indirect mechanism by which prolonged hypoxia reduces growth in turbot and sea bass, and may be a way to reduce energy and thus oxygen demand

The threat of fishing to highly fecund fishes

Abstract: The last decade has witnessed a growing awareness that fishes can not only be severely overfished but could also be threatened with extinction through over-exploitation. Among commercially important species, those particularly at risk are large and slow to mature, iteroparous and may have sporadic recruitment. The threat of extirpation or extinction may be greater if species are particularly valuable, have a limited geographical range, are part of mixed-species fisheries, or are distributed solely within areas of intense fishing activity. Significantly, there is little empirical or theoretical basis for hypothesizing that highly fecund species are any less at risk than those of low fecundity, as is often assumed. Indeed, the use of fecundity in estimating reproductive output in long-lived, highly fecund, pelagic egg-producing species, may be deeply flawed. A general resistance to accepting that fecund marine fishes could become endangered through exploitation stems from poor understanding of population dynamics, especially in the early post-settlement phase, coupled with assumptions of fishery models that ignore critical components of life history theory. Moreover, faith in the ability to manage exploited species effectively leads to the perception that severe declines are management, rather than conservation, issues. The growing list of threatened marine species and a realization of the many factors that place them at risk indicate the need to be precautionary about the possibility of extinction, and about the criteria used to assess such risk, with important implications for research, monitoring and management.

Dynamics of the shallow‐water fish assemblage of the Patos Lagoon estuary (Brazil) during cold and warm ENSO episodes

Abstract: In southern Brazil, cold (La Nina) and warm (El Nino) episodes of the El Nino Southern Oscillation (ENSO) phenomenon cause drought and high rainfall, respectively. The low precipitation and freshwater outflow associated with La Nina during 1995–1996 were associated with an increase in the abundance of marine species in the Patos Lagoon estuary. During the 1997–1998 El Nino, high precipitation and river discharge were associated with low abundance of marine species in the estuary. ANOVA results showed a higher abundance during La Nina than El Nino for estuarine resident (RES) and estuarine dependent (DEP) fishes. During La Nina catch per unit of effort (CPUE) of RES increased from the marine to estuarine area, but during El Nino CPUE increased at the marine area and diminished during summer and autumn in some estuarine sites. DEP fishes had an opposite abundance pattern. During La Nina, these fishes were abundant at the coastal marine area and along some estuarine sites, but during El Nino, CPUE remained almost the same at the marine area but dropped along some estuarine sites. These different abundance patterns for dominant fish groups yielded a positive interaction between stations and climatic events. With higher river discharge and the consequent decline of dominant euryhaline fishes, such as Mugil platanus and Atherinella brasiliensis, freshwater species increased in abundance and richness in the shallow waters of the stuary. The ENSO phenomenon influences precipitation and estuarine salinity in southern Brazil and thereby seems to have a strong influence on recruitment, immigration, and emigration dynamics of fish species living within and adjacent to estuarine habitats.

Growth and physiological changes during metamorphosis of Senegal sole reared in the laboratory

Abstract: The metamorphosis of Solea senegalensis was studied in larvae reared at 20° C and fed four different feeding regimes. A, Artemia (4 nauplii ml 1 ); B, Artemia (2 nauplii ml -1 ); C, mixed diet (2 nauplii ml -1 and 3 mg ml -1 microencapsulated diet); and D, microencapsulated diet (3.7 mg ml -1 ) Rotifers were also supplied in all cases during the first days of feeding. These feeding regimes supported different growth rates during the pre-metamorphosis period (regime A, G=0.376 day -1 ; regime B, G=0.253 day -1 ; regime C, G=0.254 day -1 ; regime D, G=0.162 day -1 ). Larvae started metamorphosis 9 days after hatching (DAH) when fed the regime A, 13 DAH with regime B, 11 DAH with regime C and 15 DAH with regime D. A minimum 5.6-5.9 mm L T was required under all feeding regimes to initiate the metamorphosis. Eye translocation was completed when the larvae reached 8.6-8.7 mm L T (regimes A, B and C), but only 7.3 mm L T with regime D, 4.4-6.2 days were required to complete eye migration under the regimes A, B and C, and 18.3 days under the regime D. This transformation is concomitant with changes in body reserves, and with the pattern of some digestive enzymes.

The importance of managing within-species diversity in cod and herring fisheries of the north-western Atlantic

Abstract: The spatial structure of several exploited species within and among known populations of the Northwest Atlantic is reviewed using past and current knowledge. For each species, the coherence of existing management units with the spatial scale of population dynamics (populations, sub-populations, and spawning components) is summarized. The implications of this match or mismatch of spatial scales in the maintenance of biodiversity within and among populations are also discussed.

Performance of stationary and portable passive transponder detection systems for monitoring of fish movements

Abstract: A stationary system for long-range detection of PIT tags in fish was efficient under high water conditions in streams. A portable system was particularly effective for detecting habitat use by fish without recapture.

Characterizing diversity in salmon from the Pacific Northwest

Abstract: Information developed during recently completed evaluations of the status of seven species of anadromous Pacific salmonids (Oncorhynchus spp.) in the Pacific Northwest was used to characterize patterns of intraspecific diversity along three major axes: ecology, life history and biochemical genetics. Within the study area, the species' ranges, and therefore the number of distinct ecological regions inhabited differ considerably, with pink and chum salmon limited to the northern areas and chinook salmon and steelhead distributed over the widest geographic range. The species showed comparable differences in the patterns of life history and genetic diversity, with chinook and sockeye salmon and steelhead having the most major diversity groups and pink, chum and coho salmon having the least. Both life history and genetic diversity showed a strong, positive correlation with the extent of ecological diversity experienced by a species, and the correlation between the number of major genetic and life history groups within a species was even stronger (r=0.96; P<0.05). Departures from these general diversity relationships found in some species (especially sockeye and coho salmon and cutthroat trout) can be explained by different interactions with the freshwater environment and, for cutthroat trout, by the occurrence of substantial intrapopulational diversity in life history traits, a hierarchical level not considered in this study.

Compensatory growth in the gibel carp following feed deprivation: temporal patterns in growth, nutrient deposition, feed intake and body composition

Abstract: To investigate the nature of compenstory growth in fish, an 8 week study at 28 degreesC was performed on juvenile gibel carp Carassius auratus gibelio weighing 6.6 g. Fish were starved for 0 (control), 1 (Sl)or 2 (S2) weeks and then re-fed to satiation For 5 weeks. Weekly changes in weight gain, feed intake and body composition were monitored during re-feeding. No significant difference was found in final body weight between the three groups, indicating complete compensation in the deprived fish, The deprived groups caught up in body weight with that of the control after 2 weeks of re-feeding. Body fat:lean body mass ratio was restored to the control level within 1 week of re-feeding. In the re-feeding period, weekly gains in body weight, protein. lipid, ash and energy in the S1 group were significantly higher than in the controls for 1 week. For the S2 group, weekly gains in body weight. lipid. ash and energy were higher than in the controls for 2 weeks, and gain in protein was higher than in the controls for 3 weeks, though gain in body energy became elevated again during the last 2 weeks of the experiment. Feed intake remained higher than the control level for 3 weeks in the S1 group and 3 weeks in the SZ group. Growth efficiency was not significantly different among the three groups in any of the weeks during re-feeding. Compensatory responses in growth and especially feed intake tended to last longer than the recovery of body composition. (C) 2001 The Fisheries Society of the British Isles.

Relationship between morphology and diets of six neotropical loricariids

Abstract: Most loricariids are algivorous and detritivorous and play an important role in both the grazer and detritus food chains of neotropical waters. Relationships between morphological variation and diet were analysed in six syntopic species (Rhinelepis aspera, Hypostomus regani, H. ternetzi. H. margaritifer, H. microstomus and Megalancistrus aculeatus) fished commercially in a 10 km 2 area of the Upper Parana River upstream from the Itaipu Reservoir. Species feeding on fine grained detritus use suction to obtain food, and possess a well-developed respiratory membrane, long gill rakers, rudimentary labial and pharyngeal teeth, a thin stomach wall, and a long intestine. Species feeding on coarser material (e.g. periphyton), ingest food by scraping the substratum. Their morphological characteristics are large, strong, spatulate teeth, short gill rakers, a well-developed stomach, and a shorter intestine, The first species group is composed by R. aspera while the latter by M. aculeatus and H. microstomus. The others species had an intermediary position.

Fertilization dynamics in sockeye salmon and a comparison of sperm from alternative male phenotypes

Abstract: Sockeye salmon Oncorhynchus nerka sperm maintained high fertility for 10 s after being exposed to water but fertility dropped sharply after that Eggs also showed limited longevity after being immersed in water, with a large drop in fertility occurring after 20 s of exposure to water The association between eggs and sperm occurs very rapidly 80% fertilization success was achieved with 5 s of sperm-egg mixing and c 25% was achieved with <05 s of sperm-egg mixing Sperm from different male age classes differed little in motility and did not differ at all in their propensity to fertilize eggs The results have important implications for mate choice and sperm competition

A histological description of intersexuality in the roach

Abstract: This paper is an illustrative guide to intersex in the roach Rutilus rutilus, based on 150 intersex individuals. Most intersex roach had female germ cells, or oocytes, within a predominantly male gonad (testis), and/or malformed/intersex reproductive ducts. The number, pattern and developmental stage of oocytes within testicular tissue in intersex fish varied greatly. In most intersex fish, a few primary oocytes, or numerous primary and secondary oocytes, were scattered randomly throughout the testicular tissue (multifocal intersex). In other, more severely feminized individuals, large areas of ovarian tissue were separated clearly from testicular tissue (focal intersex). Almost all intersex individuals had a female-like reproductive duct (ovarian cavity). In mild cases of intersex (in which the majority of the germ cells were male) the ovarian cavity was present together with the male sperm duct/vas deferens, whilst in certain severe cases, the sperm duct was absent or vestigial.

Stress induced by hooking, net towing, elevated sea water temperature and air in sablefish: lack of concordance between mortality and physiological measures of stress

Abstract: In a series of laboratory studies designed to simulate byeatch processes, sablefish Anoplopoma limbria were either hooked for up to 24 h or lowed in a net for 4 h and then subjected to an abrupt transfer to elevated sea water temperature and air. Mortality did not result from hooking or net towing followed by exposure to air, but increased for both capture methods as fish were exposed to elevated temperatures, rellecting the magnifying effect of elevated temperature on mortality. Hooking and exposure to air resulted in increased plasma corrisol and lactate concentrations, while the combination of hooking and exposure to elevated temperature and air resulted in encreased lactate and potassium concentrations. In fish that were towed in a net and exposed to air, cortisol, lactate, potassium and sodium concenrations increased, but when subjected to elevated temperature and air, ne further increases occurred above the concentrations induced by ter towing and air, suggesting a possible maximum of the physiological stress responise. The results suggest that caution should be exercised when using physiological measures to quantify stress induced by capture and exposure to elevated temperature and air, that altimately result in mortality, since the connections between physiological stress and mortality in bycatch precesses remain to be fully understood.

Feeding ecology and growth of O‐group flatfish (sole, dab and plaice) on a nursery ground (Southern Bight of the North Sea)

Abstract: The food composition of O-group sole Solea solea, dab Limanda limanda and plaice Pleuronectes platessa on a nursery ground at Gravelines, France, included 17-25 taxa. Sole (new settlers) fed mainly on harpacticoid copepods and when ≥ 50 mm in size, on polychaetes (Terebellidae). Dab (<40 mm) consumed mainly polychaetes (Magelonidae and Spionidae), and later amphipods, polychaetes (Spionidae) and Hydrozoa. O-group plaice diet was dominated by polychaetes (Terebellidae), crustaceans and molluscs at all sizes. O-group sole. dab and plaice did not compete for food resources, each species being specialized in different prey items. Growth rates during May-July 1998 varied between 0.5 and 0.67 mm day -1 for sole, 0.12 and 0.24 mm day -1 for dab and 0.55 and 0.81 mm day -1 for plaice. For sole and plaice, these estimates were similar to those recorded in other nurseries and also close to the maximal growth predicted by experimental models. This suggests that their growth was not limited by food during the first summer of life.

Reproduction in the dusky grouper from the southern Mediterranean

Abstract: Demographic data and gonad histology confirmed that the dusky grouper Epinephelus marginatus is a protogynous hermaphrodite that follows a monandric pathway to sexual development. Females reached first sexual maturity at 36.7 cm L S and estimated mean length at first maturity (L 50 ) was 43.8 cm L S for females and 81.3 cm L S for males. Adult sex ratios during the reproductive period were c. 3.5: 1 females to males. Females exhibited group-synchronous ovarian development and multiple ovulation occurred over the spawning period. Gonads were ripe from early May and spawning occurred from June until early September. The size of ripe testes (0.6% W) indicated strong oligospermy and suggested a mating system with no sperm competition. Sexual transition was protogynous involving regression of ovarian tissue and proliferation of testicular tissue in the gonads. Transitional individuals occurred from May through November and accounted for 9% of sampled adult population. Sex change occurred in fish 69-93 cm (L S ) long and the size distributions of males and females overlapped over 27% of the L S range Special zones were recognized as gathering areas for sexually mature dusky groupers during the reproductive period.

Anatomical features and histology of the digestive tract of two related neotropical omnivorous fishes (Characiformes; Anostomidae)

Abstract: The estimated mean intestinal coefficients of Leporinus friderici Bloch. 1794 and L. taeniofasciatus Britski, 1997, from the Upper Tocantins River, central-western Brazil, were 1.25 ± 0.15 and 1.14 ± 0.07, respectively. The external surfaces of the lips have taste buds. The histological structure is composed of four layers: mucosa, submucosa, muscular, and serosa. No muscularis mucosa is detected. The oesophageal epithelium is stratified in L. friderici and pseudostratified in L. taeniofasciatus, the latter with PAS + basal cells and eosinophilic apical cells. A thick layer of adipose tissue was found within the submucosa. Leporinus taeniofasciatus has a sphincter separating the cardiac and fundic portions of the stomach. In both species, gastric glands are present in the stomach, except in its pyloric portion. The pyloric caeca possess a simple columnar epithelium with brush border and three types of goblet cells. Rodlet cells were found in L. friderici. The three portions of the intestine showed no histological differences. Anatomical and histological features of the digestive tract are consistent with the omnivorous habit of both these species.

Social status, access to food, and compensatory growth in juvenile Atlantic salmon

Abstract: Juvenile Atlantic salmon Salmo salar subjected to three weeks of cooler temperatures were 8·5% smaller than controls at the end of the temperature manipulation, but had caught up in size 20 weeks later. The behavioural means is examined by which this catch-up or compensatory growth is achieved. While on average compensating fish did not spend more time feeding, dominant fish within each group gained more exclusive access to the feeding area during periods of catch-up growth. Therefore the extent to which compensatory growth could be achieved was dependent on both the social status of the individual and the dominants’ ability to monopolize the food patch.

The influence of fish size on the avoidance of hypoxia and oxygen selection by largemouth bass

Abstract: When an oxygen gradient ranging from c. 10 to 95% air saturation was formed in a 5 m chamber, largemouth bass Micropterus salmoides avoided water in which dissolved oxygen values were <27% air saturation. There was a significant (P<0·05) correlation between fish mass and the level of dissolved aquatic oxygen that was selected. Small fish (23–500 g) utilized waters of lower oxygen levels than did the larger fish (1000–3000 g). The results of this study suggest that largemouth bass are able to sense and avoid hypoxic water, and select aquatic oxygen tensions that maintain their metabolic scope for growth and activity.

Seasonal variations in the energy density of fishes in the North Sea

Abstract: The energy density (E D , kJ g -1 wet mass) of saithe Pollachius virens, haddock Melanogrammus aeglefinus, whiting Merlangius merlangus, Norway pout Trisopterus esmarki, herring Clupea harengus, sprat Sprattus sprattus, sandeel Ammodytes marinus and pearlsides Maurolicus Muelleri, from the North Sea, increased with total length, L T . However, there was not always a significant (P>0.05) linear relationship between L T and E D . Seasonal differences in E D were obvious in mature fish, while geographical differences were insignificant. For all species there was a highly significant correlation (P<0.0001) between the percent dry mass of the fish (D S ) and E D . A general relationship was established for gadoids and sandeel E D = - 3.1492+0.3459 D S and herring E D = 4.6395+0.4170 D S . Thus seasonal and size-specific data on E D needed for bioenergetics and gastric evacuation models can be determined simply from D S , which is considerably less costly and time consuming than calorimetry or proximate analysis.

Return migration of Atlantic Salmon in the River Tana: Phases of migratory behaviour

Abstract: From a total of 174 multi-sea-winter Atlantic salmon radio tagged in the Tanafjord (northern Norway, 70° N) during 1992 and 1993, 48 Atlantic salmon were followed from entering the River Tana until spawning. Three phases were identified: (1) migratory, direct or stepwise migration to, or close to the position held at spawning; (2) search, movements both up and down river at or close to the position held at spawning; (3) holding, a period without movements prior to spawning. During the migratory phase, Atlantic salmon migrated directly to near the spawning area, or stopped between one and nine shorter periods during the upstream migration. Number of stops increased with increasing migratory distance in 1993, but no such correlation was found in 1992. The highest migratory speeds were recorded in the lower parts of the river. A distinct change in migratory pattern was found in 67% of the Atlantic salmon near or at the area held at spawning. Most common was a search phase of erratic movements with more than one down river movement. After the movement terminated, 96% of the Atlantic salmon had a period when no or little movement was recorded until spawning (on average 55 days in 1992 and 51 days in 1993). There was no preference for staying at, up or down river from the spawning area during this holding period. Early ascending Atlantic salmon migrated to spawning areas further from the mouth than the later arriving Atlantic salmon in 1993, but not in 1992. The proportion of time spent on the migratory phase increased, while the proportion of time spent on the holding phase decreased with increasing distance to the spawning area.

Effects of brackish water on growth, feed conversion and energy absorption efficiency by juvenile euryhaline and freshwater stenohaline fishes

Abstract: Among six species of juvenile fishes (<6 months old), stenohaline species (channel catfish Ictalurus punctatus and goldfish Carassius auratus) had their highest specific growth rate (G) and most efficient food conversion ratio (EC) and energy absorption efficiency (IE) in fresh water. Three of the euryhaline species (rainbow trout Oncorhynchus mykiss, striped bass Morone saxatilis and Gulf sturgeon Acipenser oxyrinchus desotoi) had higher G and had more efficient EC and IE in 3 and 9‰ salinities than in lower salinities (fresh water and 1‰). For brown trout Salmo trutta (age 3–4 months), 9‰ was above the optimum level for G and E C. However, IE for brown trout was not significantly different at 3 and 9‰ salinities. Over the salinity range tested, channel catfish had the largest change in G, EC and IE, while changes for euryhaline species were relatively small. Although all species tested survived and grew in all treatments, salinities as low as 1‰ adversely affected the stenohaline species, and 9‰ adversely affected brown trout.

Plasma cortisol and metabolite level profiles in two isogenic strains of common carp during confinement

Abstract: A rapid increase in common carp Cyprinus carpio plasma cortisol levels was noted, in two experiments, after 30 mins of a 3 h net confinement, which was sustained while the fish were held in the nets. After release from the nets, cortisol levels returned to control values in 1 h. Plasma glucose and free fatty acid levels were elevated by the confinement. Glucose was increased after 30 min but returned to basal levels after 22 h of recovery while free fatty acids were not elevated until 3 h of confinement and remained high for the duration of the recovery period. After confinement for 3 h, plasma lactate levels were reduced and remained low for a further 1 h. No change in either plasma triglyceride or cholesterol levels were found during the study. Confinement had no effect on haematocrit levels but blood haemoglobin levels were reduced. In both experiments hypochloraemia occurred in response to confinement. However, values returned to pre-confinement levels 22 h after confinement. These results show that rearing isogenic carp strains, under identical conditions, results in a reproducable response to an acute stressor and that these carp respond in a similar manner to other teleost species.

Associations between fish assemblages and environmental factors in nearshore habitats of a subtropical estuary

Abstract: Salinity and inlet distance were the most consistent indicators of species groupings among the 40 most abundant fish species in the Indian River Lagoon (IRL), Florida. In contrast to findings of other studies conducted on small juveniles and forage fishes in the IRL, this study suggested that distributions of the more mobile organisms are influenced more by physical conditions than by biological interactions. Consequently, environmentally-corrected single-species models will be more effective in assessing changes in stock abundance and habitat preferences of mobile species in the IRL. Because of the fluctuations in physical conditions in the IRL and other estuaries, it may be inappropriate to use biologically based methods that rely solely on species interactions to assess fish stocks in those systems.

The effect of light intensity and spectrum on the incidence of first feeding by larval haddock

Abstract: Under full–spectrum white light, feeding success of haddock Melanogrammus aeglefinus first feeding larvae, as measured both by proportion of larvae feeding and mean prey consumed, peaked at 1·7-18 μmol s-1 m-2. Feeding was significantly reduced at lower and higher intensities. A similar result was observed for larvae feeding under blue (470 nm) light, with significantly greater feeding success at intermediate light intensity (1·8 μmol s-1 m-2). When different light qualities were compared, larvae had significantly greater feeding success when exposed to blue (470 nm) light than either full-spectrum white or green (530 nm) light. Haddock larvae were capable of prey capture under all light treatments tested, indicating a necessary degree of adaptive flexibility in feeding response. The results are consistent with predisposition of haddock larvae to optimal feeding in a visual environment comparable with open ocean nursery grounds. Information on the impact of light on haddock first feeding can be incorporated into models of larval growth, survival, year-class strength and recruitment, and assist in developing husbandry protocols to maximize larval survival in aquaculture.

Home range size and use of space by Bermuda chub Kyphosus sectatrix (L.) in two marine reserves in the Soufrière Marine Management Area, St Lucia, West Indies

Abstract: Marine reserves (MRs) are expected to conserve fish biodiversity and enhance fisheries production of surrounding areas through export of adult fish biomass. However, the extent to which these benefits occur is dependent on movement patterns of fish, for which there is a paucity of data, particularly for coral reef species. Eleven adult Kyphosus sectatrix were tracked [five in the Grand Caille marine reserve (MR) and six in the Petit Piton MR within the Soufriere Marine Management Area, St Lucia] from February to April 1999, using acoustic telemetry. Average number of days over which fish were tracked was 21.5 (range 5-51). Home range size of individuals, temporal use of space within the home range, and permeability of MR and habitat boundaries to fish movement were examined. Average minimum home range area of K. sectatrix was not significantly different between Grand Caille (30 514 m 2 ) and Petit Piton (39 114 m 2 ). However, the shape of home ranges was conspicuously different between the sites and reflected available reef shape. Individual home ranges overlapped strongly with those of other individuals at the same site, and use of space within the home range was generally restricted to a small number of preferred sites. Preferred sites were often shared among individuals and tended to be occupied at a specific time of day, with some sites were preferred in the morning and or afternoon, whilst others preferred during the middle of the day. Fidelity to a single sleeping-shelter site was high at night. MR boundaries over contiguous reef at Grand Caille were frequently crossed with individuals spending, on average, 63% of their time (range 37-94) outside the MR. This demonstrates the need for the MR boundary at this site to be implemented farther offshore to encompass the reef, if the MR is to better protect K. sectatrix. At Petit Piton, where MR boundaries effectively encompass available reef, K. sectatrix spent, on average, only 11% of their time (range 0-40) outside the protected area. At Grand Caille boundaries were crossed more readily (individuals spent an average of 18% of their time off reef) than at Petit Piton where individuals spent an average of 0.7% of their time off reef.