Showing papers in "Journal of Fish Biology in 1987"
TL;DR: Physiological adaptation of the cardiovascular system of rainbow trout to changes in acclimation temperature is demonstrated by increasing linearly with increasing temperature.
Abstract: Cardiac output, blood flow distribution and regional perfusion were determined in free-swimming rainbow trout acclimated to 6, 12 and 18°C, using the indicator dilution and microsphere methods. Cardiac output (ml min−1 kg−1) increased linearly with increasing temperature, while circulation time decreased. Blood flow distribution (% of cardiac output) to the spleen, liver, kidney, gall bladder and gastro-intestinal tract was significantly reduced at 18°C relative to 6°C-acclimated fish. White muscle received the largest fraction of cardiac output, and blood flow distribution to white muscle increased significantly with increasing acclimation temperature. Blood perfusion (ml h−1 g−1) of various organs and red muscle was not influenced by acclimation temperature, while white muscle perfusion increased with increasing temperature. These results demonstrate physiological adaptation of the cardiovascular system of rainbow trout to changes in acclimation temperature.
179 citations
TL;DR: It is suggested that stream-dwelling trout suffer a metabolic deficit during acclimation to rapidly declining water temperatures in November/December, which has important physiological implications for overwinter survival.
Abstract: The feeding of brook and brown trout in a temperate Canadian stream was studied over two winters. Stomach analyses indicate that feeding continues throughout the winter. Both species had similar diets. Despite continuous feeding, condition factors declined significantly in early winter and remained low until the spring, suggesting an early-winter depletion of lipid reserves. Energy (calorific) intake was similar in winter to that found in late summer or spring and therefore was not the cause of low winter condition. The derived energy from feeding was insufficient to offset the costs of maintenance metabolism in the early winter period, for both immature and recently spawned fish. It is suggested that stream-dwelling trout suffer a metabolic deficit during acclimation to rapidly declining water temperatures in November/December. Such a phenomenon has important physiological implications for overwinter survival.
169 citations
TL;DR: It is suggested that differences in surface-to-volume ratios between large and small food particles and the friabilities of different food types are important in determining the pattern of emptying.
Abstract: The evacuation of food from the stomach is probably not a continuous smooth process but may occur in a pulse-like (step-wise) fashion. It is hypothesised that the pattern of emptying is influenced by feedback signals from receptors located in the upper intestinal tract and by factors affecting the rate of physical/chemical breakdown of the food particles. Mathematical functions used for describing evacuation patterns imply that emptying is continuous and they are, therefore, at best, only approximations. It was predicted that different mathematical expressions would give best fit to empirical data from gastric evacuation studies dependent upon the experimental conditions employed. An analysis of published data supported the predictions and revealed that an exponential function best described the evacuation of small, easily digested prey items, but a linear expression gave the best fit to data of the emptying of large food items. It is suggested that differences in surface-to-volume ratios between large and small food particles and the friabilities of different food types are important in determining the pattern of emptying. Whilst dietary energy content also appears to be an important factor in the governing of gastric evacuation, it appears that emptying pattern in fish species is rather less sensitive to changes in dietary composition than is gastric emptying in mammals.
155 citations
TL;DR: The presence and localization of acid and alkaline phosphatase, non-specific proteases, aminopeptidase, amylase, Non-specific esterase and lipase was investigated by histoenzymologic methods in fed and fasting turbot from day 1 to day 40 post-hatching and compared with published data.
Abstract: The presence and localization of acid and alkaline phosphatase, non-specific proteases, aminopeptidase, amylase, non-specific esterase and lipase was investigated by histoenzymologic methods in fed and fasting turbot from day 1 to day 40 post-hatching and compared with published data. Alkaline phosphatase and aminopeptidase activities were delected at day 1 in the distal region of the developing digestive tube. At day 3 (opening of the mouth) aminopeptidase and alkaline phosphatase activities were found all along the intestine. Sites of non-specific esterase and protease activities became apparent in the digestive tract at days 2 and 3 respectively. Amylase was present in the exocrine pancreas at day 3 and in the lumen of the intestine at day 4. Acid phosphatase was active in the cellular structure surrounding the yolk stores and in the lipid droplets at day 1 and in the intestinal epithelium at day 3. Lipase was found at day 15 when the larvae metamorphose into juveniles.
All the investigated enzymes were detected in fasting animals, except for lipase. However, the intensities of the enzymatic activities were weaker in the fasting specimens relative to the fed specimens between days 7 and 10.
150 citations
TL;DR: It is concluded that changes in the composition of circulating blood cells are more reliable indicators of chronic crowding stress than are plasma cortisol levels.
Abstract: Crowding for 3 weeks significantly reduced the coefficient of condition of both brown trout and rainbow trout. However, acclimation of the hypothalamic-pituitary-interrenal (HPI) axis, as assessed by changes in plasma cortisol levels, occurred within 6 days for brown trout and within 10 days for rainbow trout. Blood lactate levels were significantly reduced in the crowded fish of both species throughout the experiment. Sexual maturation of the male fish significantly elevated the number of circulating red blood cells in both species, reduced the lactate levels in brown trout and elevated cortisol levels in the rainbow trout. Despite the relatively rapid interrenal acclimation, the numbers of thrombocytes and lymphocytes in the blood of both species were significantly reduced during the period of crowding and it is concluded that changes in the composition of circulating blood cells are more reliable indicators of chronic crowding stress than are plasma cortisol levels. These findings are discussed in relation to the role of the HPI axis in suppressing the defence systems of salmonid fish during periods of chronic stress.
146 citations
TL;DR: Two herbivorous fishes of the genus Kyphosus possess unique digestive tracts among fishes, with well-developed caecal pouches and a complex gut-resident microflora that confirms fermentative digestion in fishes for the first time.
Abstract: Two herbivorous fishes of the genus Kyphosus (family Kyphosidae) possess unique digestive tracts among fishes, with well-developed caecal pouches and a complex gut-resident microflora. The presence of high concentrations of volatile fatty acids in the gut confirms fermentative digestion in fishes for the first time.
137 citations
TL;DR: The feeding relationships of an assemblage of demersal fishes present on a soft-sediment bottom off the west coast of Scotland in the late summer-autumn were investigated and three major feeding types could be distinguished.
Abstract: The feeding relationships of an assemblage of demersal fishes present on a soft-sediment bottom off the west coast of Scotland in the late summer-autumn were investigated. On the basis of stomach content analyses of the fifteen commonest species, three major feeding types could be distinguished. The first consisted of small browsing species feeding predominantly on infaunal polychaetes. The second relied heavily on caridean decapods, but within this group three subgroups could be detected which supplemented their diet with amphipods, mysids or polychaetes, respectively. The third group fed on large prey consisting of mysids and/or fish. Several species passed from one group to another as they grew, and there was a general tendency for fish to become more specialized in their diet with increasing size. The three groups represent a series in which decreasing reliance is placed on the substratum as a source of food.
120 citations
TL;DR: The cortisol response of both brown trout and rainbow trout to acute confinement was suppressed in a manner similar to that observed with trout at high densities, and a compensatory increase in plasma cortisol levels was observed during the subsequent recovery of fish which had been confined for 1 h in water of poor quality.
Abstract: Confinement of brown trout in small troughs of static water for 1 h at a density of six fish per 25L stimulated the hypothalamic-pituitary-interrenal axis and resulted in an elevation of plasma cortisol from basal levels (less than 2 ng/ml) to about 100 ng/ml, the degree of stimulation being dependent upon water temperature. Confinement at a density of 30 fish per 25L resulted in a 50% suppression of this response. It is demonstrated that this effect is mediated by changes in water chemistry and not by crowding per se. Experimental manipulation of the water chemistry showed that reduced pH (7.1 to 6.3), elevated free CO2 (63 to 520 μmol/L) or elevated ammonia (8 to 1300 μg/L as total ammonia nitrogen) had no individual effects on the interrenal response to acute confinement. Elevated ammonia in combination with reduced pH significantly increased the plasma cortisol levels in response to acute confinement, whereas a combination of reduced oxygen (100 to 20% saturation), elevated free CO2 and elevated ammonia markedly suppressed (∼ 50%) the cortisol response of both brown trout and rainbow trout to acute confinement in a manner similar to that observed with trout at high densities. A compensatory increase in plasma cortisol levels was observed during the subsequent recovery of fish which had been confined for 1 h in water of poor quality. These findings are discussed in relation to the exposure of fish to multiple stresses and to the role of corticosteroids in the stress response.
114 citations
TL;DR: The post-smolt stage of salmon, Salmo salar L., is subject to heavy mortality in Norway, and each year 35 000 hatchery-reared smolts are stocked in the River Surna, which results in recovery rates of adult salmon which are up to three times better than those resulting from river stockings.
Abstract: The post-smolt stage of salmon, Salmo salar L., is subject to heavy mortality in Norway. Each year 35 000 hatchery-reared smolts are stocked in the River Surna. Smolt stocking at sea and in the fjord resulted in recovery rates of adult salmon which were up to three times better than those resulting from river stockings. This was supposed to be due to by-passing some predators. In 1984 and 1985 predators and their predation on smolts were studied in the R. Surna estuary. Cod, Gadus morhua, were found to prey heavily on smolts, and a total mortality up to 24.8% was found in a small restricted area. Cod are thought to assemble in the Surna estuary in the spring, foraging on the smolt run.
111 citations
TL;DR: The gut contents of 37 species of Nile fish are described and food webs are proposed for three major ecological zones, namely the open-water and submerged vegetation of a river-lake, the floating fringe of Eichhornia crassipes and the seasonally flooded grassland.
Abstract: The gut contents of 37 species of R. Nile fish are described. Classification according to diet shows four species to be mud-feeders, three to be microherbivores, two to be macroherbivores and five to be omnivores. The remaining majority (23) are categorized as carnivorous and comprise one neuston-feeder, one zooplanktivore, six bottom-feeders, seven browsers in vegetation and eight macropredators. Food webs are proposed for three major ecological zones, namely the open-water and submerged vegetation of a river-lake, the floating fringe of Eichhornia crassipes and the seasonally flooded grassland.
109 citations
TL;DR: After varying periods of food deprivation the foraging behaviour of parasitized and non-parasitized sticklebacks was measured in both undisturbed and recently frightened fish.
Abstract: After varying periods of food deprivation the foraging behaviour of parasitized and non-parasitized sticklebacks was measured in both undisturbed and recently frightened fish. Parasitized sticklebacks forage significantly more actively and recover more quickly after a frightening stimulus than do control fish. They also react more quickly to food deprivation than do uninfected control fish. Seventy-two hours without food is sufficient to suppress the fright response in parasitized fish, and causes them to forage at the same rate as when undisturbed. Non-infected controls failed to forage successfully after a frightening stimulus, even when they had been without food for 96 h. Frightening stimuli can affect profoundly the normal foraging behaviour of hungry fish.
TL;DR: The phagocytosis of neutrophils and serum lysozyme activity were investigated in carp experimentally infected with Pseudomonas alcaligenes and Aeromonas punctata and there was a significant increase of the NBT test rate, NBT reduction and Lysozyme index.
Abstract: The phagocytosis of neutrophils and serum lysozyme activity were investigated in carp experimentally infected with Pseudomonas alcaligenes and Aeromonas punctata. The total leucocyte numbers, relative leucocyte counts, nitroblue tetrazolium (NBT) reduction, NBT test rate, lysozyme activity and lysozyme index were examined on days 7, 14 and 21 after injection. On days 7 and 14 there was a significant increase in total leucocyte numbers and serum lysozyme activity, but a decrease in the NBT test rate and lysozyme index. NBT reduction was unchanged compared with the control group. On day 21 the total leucocyte numbers and lysozyme activity had declined and were less than control values, but there was a significant increase of the NBT test rate, NBT reduction and lysozyme index.
TL;DR: Fertility tests on frozen tilapia milt resulted in a fertilization rate of 72.7% (v. control 85.7%) for the 22-day frozen milt of the O. aureus hybrid used to fertilize the eggs of O. honorum, and 93.4% ( v. control 90%) for
Abstract: The specific differences between the testis, milt and sperm of six species of tilapia including Oreochromis aureus, O. mossambicus, O. niloticus, Tilapia zillii, O. nilolicus×O. aureus hybrid and red tilapia, Oreochromis sp., were studied. The shape of testis is tubular; the gonadosomatic index varied from 0.07 to 2.71. The pH values of individual milts ranged from 6.2 to 8.2 and the osmolarity from 240 to 380 mOsmol kg−1. The quantity of milt obtained by stripping averaged only about 0.3 ml, and only in the O. niloticus×O. aureus hybrid did it exceed 3 ml. Sperm motility graded from weak to moderate was determined for the stripped tilapia milt. Sperm concentrations ranged from 7.70 × 108 sperms ml−1 in T. zillii to 2.74 × 1010 sperms ml−1 in O. mossambicus. Tilapia sperm was active in various salinity ranges such as 0–5‰ for O. niloticus, and 0–15‰ for O. mossambicus and T. zillii. Extender containing 15% milk and 5% methanol was used to prepare milt mixture before cooling rapidly to −35° C and then at 5° C min−1 to −75° C for storage in liquid nitrogen (– 196° C).
Fertility tests on frozen tilapia milt resulted in a fertilization rate of 72.7% (v. control 85.7%) for the 22-day frozen milt of the O. nilolicus×O. aureus hybrid used to fertilize the eggs of O. honorum, and 93.4% (v. control 90%) for the 304-day frozen sperm of red tilapia used to fertilize eggs of red tilapia.
TL;DR: The anatomy and the histology of the digestive tract of young and adult sea-bream is described from studies using light and scanning electron microscopy.
Abstract: The anatomy and the histology of the digestive tract of young and adult sea-bream is described from studies using light and scanning electron microscopy. The dentition in the juvenile (25–30 mm long) comprises all canine-like teeth, to which plate teeth and transition elements are added in the adult.
The oesophagus shows a multi-layered mucosa in the upper part, and single-layered regions in the lower part. The multi-layered regions are formed by epithelial cells, mucus-secreting cells and by cells rich with eosinophilic granules.
The Y-shaped stomach, clearly distinguishable, has a single-layered columnar epithelium under which, in the cardiac and fundic portion, gastric glands, comprised of all similar cells, are present. The pyloric region is characterized by four caeca, to the base of which the ductus pancreaticus and the ductus hepaticus discharge.
The pancreas is composed of small masses spread along the upper intestine; in the adult, pancreatic infiltrations can be seen in the liver.
The intestine is short (relative length 0.5–0.6). The intestine epithelium consists of columnar cells intercalated with mucus-secreting cells. A funnel-like valve marks the passage to the intestine terminal region, characterized by a mucosa of cells with an abundance of vacuoles full of eosinophilic granules.
TL;DR: No significant difference in length distribution was found between the sea trout caught in the Vardnes river and those caught in other rivers, and an hypothesis concerning the selective advantages of straying by anadromous salmonids living in small rivers is discussed.
Abstract: During the periods 1956–1963 and 1967–1970 traps were operated to catch upstream- and downstream-migrating sea trout, Salmo trutta L. A total of 15 788 sea trout were tagged, using Carlin tags. The number of recaptures made in the traps was 4481, of which 1796 were recaptured more than once.
The distribution of the 2122 recaptures in the sea provides a picture of the sea-migration pattern. Of the sea recaptures, 52.8% were reported as within a distance of 3 km from the river mouth, compared to 0.7% more than 80 km away. All the different size-groups of sea trout were represented among both the long-distance and the short-distance migrants. The results of this study of sea trout migrations are discussed in relation to the published results for Atlantic salmon, Salmo salar L., and sea charr, Salvelinus alpinus (L.), from the same river.
The four highest values recorded for mean distance of daily travel away from the river were 20, 8, 8 and 6km day−1 by smolts and 6, 6, 5 and 5km day−1 by larger-sized sea trout.
Recaptures of tagged sea trout in rivers other than the Vardnes totalled 506, of which 306 had been tagged as smolts. The calculated minimum percentage of stray is 15.5%. The proportion of sea trout from the Vardnes river that actually spawn in other rivers is not known. No significant difference in length distribution was found between the sea trout caught in the Vardnes river and those caught in other rivers. An hypothesis concerning the selective advantages of straying by anadromous salmonids living in small rivers is discussed.
TL;DR: Larger eels tended to attack more readily, be dominant in threat encounters, be less active and spend less time swimming high in the water, consume more food, and show higher growth rates and lower mortality.
Abstract: Agonistic behaviours were studied at high densities and in tournament experiments with pairs of small eels with and without prior isolation. Although innate differences probably exist, eels appear to learn their average positions in diffuse social and size hierarchies from the outcome of repeated agonistic encounters. Dominance or avoidance were most marked when the larger fingerling eels were about 1.5 times the body weight of the smaller. Larger eels tended to attack more readily, be dominant in threat encounters, be less active and spend less time swimming high in the water, consume more food, and show higher growth rates and lower mortality. Implications for warm-water aquaculture are discussed, and practical management techniques to minimize mortality and maximize productivity are suggested.
TL;DR: In vitro-stimulated peritoneal cells showed an increased NBT reduction and 3H-uridine incorporation over a range of Con A concentrations, compared with untreated control macrophages, but no detectable increases in H2O2 production or bactericidal activity were observed.
Abstract: Rainbow trout peritoneal macrophages were stimulated in vitro using Concanavalin A (Con A) and in vivo using formalin-killed Aeromonas salmonicida in Freund's incomplete adjuvant (FIA). Whether these cells had been activated was determined by the measurements of oxygen anions (NBT reduction), H2O2 production (oxidation of phenol red), RNA synthesis (3H-uridine incorporation), acid phosphatase activity and bactericidal activity.
In vitro-stimulated macrophages showed an increased NBT reduction and 3H-uridine incorporation over a range of Con A concentrations, compared with untreated control macrophages, but no detectable increases in H2O2 production or bactericidal activity were observed. On the other hand, in vivo-stimulated peritoneal cells showed increases in all the assays compared with FIA-elicited control cells, and were considered to have been activated.
TL;DR: Increased fishing pressure could lead to the elimination of anadromous males from some populations because the mortality associated with parr maturation already leads to a loss of 60-70% of the male production in some commercial fisheries.
Abstract: result of increased fishing pressure (Gibson, 1978; Myers, 1983). Such increases are alarming because the mortality associated with parr maturation already leads to a loss of 60-70% of the male production in some commercial fisheries (Myers, 1984). If anadromous males are not necessary for the successful spawning of anadromous females, then increased fishing pressure could lead to the elimination of anadromous males from some populations. In view
TL;DR: The literature concerning eye migration and cranial development during flatfish metamorphosis is briefly reviewed and found to give rise to five hypotheses to account for the phenomenon.
Abstract: The literature concerning eye migration and cranial development during flatfish metamorphosis is briefly reviewed and found to give rise to five hypotheses to account for the phenomenon. The cranial morphology of specimens of Soleidae, Pleuronectidae, Scophthalmidae and Bothidae in pre-metamorphic, metamorphic and post-metamorphic stages are described. The mechanisms by which eye migration and cranial development occur are discussed and some aspects of pleuronectiform relationships are briefly commented on.
TL;DR: The classic Homer Smith divided box experiment was repeated upon five marine and one freshwater teleost species, indicating that nitrogen excretion by the gills is of lesser importance in marine teleosts than in freshwater species.
Abstract: The classic Homer Smith divided box experiment (Smith, 1929) was repeated upon five marine and one freshwater teleost species. Of the nitrogenous output (as ammonia and urea), 50–70% occurred in the head region for marine teleosts, while the freshwater tilapia studied excreted 90% from the head. Together with the data of Smith, these data indicate that nitrogen excretion by the gills is of lesser importance in marine teleosts than in freshwater species.
In the dab, Limanda limanda, the head, anus and urinary opening were all in the anterior chamber of the divided box, but 47% of nitrogen excretion still occurred in the posterior chamber, presumably across the skin. In the blenny, Blennius pholis, exposed to air, the head region accounted for 46% of urea elimination, and 26% of ammonia output.
TL;DR: The natural food of Oreochromis niloticus from two Ethiopian Rift Valley lakes, Awasa and Zwai, was studied from the stomach contents to determine its chemical composition and revealed that Microcystis sp.
Abstract: The natural food of Oreochromis niloticus from two Ethiopian Rift Valley lakes, Awasa and Zwai, was studied from the stomach contents The food was analyzed to determine its chemical composition The major consumed nutrient by the Awasa population was carbohydrate whereas in the Zwai population it was lipid Microscopic identification revealed that Microcystis sp and Botryococcus braunii are the dominant algae present in the food of the fishes from Lakes Zwai and Awasa, respectively Assimilation efficiency of total organic matter is somewhat low, 283% for Awasa and 147% for Zwai populations Both populations assimilated protein to a greater extent than other nutrients In both lakes the quality of the food, expressed as a ratio of digestible protein to digestible energy, is adequate (>4 mg kJ −1) for growth, but the Awasa population appears to have higher growth and better condition
TL;DR: Feeding rhythms in juvenile sole (0- and I-groups) and differences in choice of prey according to age and feeding time are described and intermediate between estimates from Kuipers' method and those from Elliott & Persson's model.
Abstract: This study describes feeding rhythms in juvenile sole (0- and I-groups) and differences in choice of prey according to age and feeding time. In the same biotype, 0-group fish select amphipods or young opisthobranchs, whereas I-group fish eat chiefly polychaetes such as Pectinaria koreni. The daily food consumption for juvenile soles in the field (T = 19.8°C) is estimated at 7% body dry weight in 0-group and probably less in I-group. When compared with estimates from previous methods or models, these rations are intermediate between estimates from Kuipers' method, with a gastric evacuation rate (R) per hour representing three times the amount of food in the stomach, and those from Elliott & Persson's model with R value around 1.46.
TL;DR: Sera from channel catfish rendered immune to the protozoan pathogen Ichthyophthirius multifiliis were screened for activity against live parasites and the involvement of humoral antibodies in agglutination and protective immunity is discussed.
Abstract: Sera from channel catfish rendered immune to the protozoan pathogen Ichthyophthirius multifiliis were screened for activity against live parasites. Cells in the infective stage (tomites) were incubated in doubling dilutions of immune and pre-immune sera from fish that had been immunized by exposure to sublethal infections. When examined by light microscopy, tomites were found to agglutinate in the presence of immune sera. While the stength of individual sera varied, agglutination of cells occurred at dilutions as high as 1:128. Cells showed little tendency to agglutinate in pre-immune sera, and virtually no effects were seen with dilutions of pre-immune sera greater than 1:16. Agglutination was usually accompanied by release of mucus from cells, and while tomites appeared to be immobilized, their cilia continued to beat. Low dilutions of immune sera appeared to be toxic. Similar effects on tomites were seen with rabbit antisera prepared against Ichthyophthirius cilia. The involvement of humoral antibodies in agglutination and protective immunity is discussed.
TL;DR: The study suggests that MMC formation in this instance is an inflammatory process in which mononuclear phagocytes recruited from peripheral circulation play a dominant role.
Abstract: Formation of hepatic melano-macrophage centres (MMCs) in Rivulus marmoratus was induced with the coccidian parasite Calyptospora funduli. Experimental infections were produced by feeding infected intestine and hepatopancreas from grass shrimp (Palaemonetes pugio) to individual parasite-free fish. Livers of fish sampled 5–150 days post-infection were examined histologically. Mild diffuse inflammation initiated during early merogony (5–8 days) consisted of eosinophilic granulocytes and heterophils. Liberation of merozoites (8–12 days) caused extensive hepatocyte degeneration and augmented leucocyte exudation. During gamogony (15–18 days) mononuclear phagocytes became a predominant component of the cellular exudate. Focal lesions, considered to be early MMCs, became apparent during early sporogony (20–25 days); they consisted of degenerating infected hepatocytes and inflammatory cells, and contained developing oocysts and degenerating macrogamonts, but no pigment. Early centres became visible grossly at 30 days as diffuse, yellow-tan foci within the hepatic parenchyma. Pigment content increased progressively, but melanin was never a major component. Oocysts first elicited a granulomatous response between 40 and 50 days. The study suggests that MMC formation in this instance is an inflammatory process in which mononuclear phagocytes recruited from peripheral circulation play a dominant role. MMC development appears to be elicited by macrogamont degeneration, whereas granuloma formation is probably a response to oocysts.
TL;DR: Methods for the collection, fixation, preservation and examination of the cestodes parasitic in British freshwater fishes are described and an illustrated key to the species is provided.
Abstract: Methods for the collection, fixation, preservation and examination of the cestodes parasitic in British freshwater fishes are described. An illustrated key to the species is provided, with the exception of the members of the genus Proteocephalus, for which the information is tabulated.
TL;DR: Winter flounder from known locations were sorted according to their reproductive status about 4 weeks before spawning, and fish fed to satiation included some which had been initially designated non-reproductive post-mature.
Abstract: Winter flounder from known locations were sorted according to their reproductive status about 4 weeks before spawning. Five groups were then fed to satiation and three groups were not fed. The experiment was terminated at the end of the summer feeding season. At termination, only one of the recently spawned fish with restricted feeding showed gonad recrudescence. Conversely, all previously reproductive fish which had been fed to satiation showed gonad recrudescence. Fish fed to satiation included some which had been initially designated non-reproductive post-mature. These experiments indicate that a non-reproductive post-mature state is inducible and may be reversible, with the switch related to nutritional status.
TL;DR: The diets and feeding periodicities of two small, riffle-dwelling fish, the torrentfish and the bluegilled bully, were investigated in an unstable, braided New Zealand river and it was indicated that the feeding periodicity of the two species differed.
Abstract: The diets and feeding periodicities of two small, riffle-dwelling fish, the torrentfish, Cheimarrichthys fosteri, and the bluegilled bully, Gobiomorphus hubbsi, were investigated in an unstable, braided New Zealand river from May 1985 to April 1986. Aquatic insect larvae dominated diets of all fish and dietary overlap between species was high in 10 of 12 months. Nevertheless, the relative importance of prey items, as assessed by the index of relative importance (IRI), differed between species. Gobiomorphus hubbsi fed almost exclusively on larval Deleatidium (Ephemeroptera), whereas C. fosteri consumed a greater variety of prey items, with Deleatidium and trichopteran, elmid and chironomid larvae numerically dominant. A dietary switch from Deleatidium to chironomid larvae occurred in both species during December 1985, when total and relative abundances of mayfly and other benthic macroinvertebrate larvae were severely reduced by two consecutive floods. A diel sampling programme indicated that the feeding periodicity of the two species differed: C. fosteri was a nocturnal feeder, whereas G. hubbsi exhibited a strong crepuscular peak in feeding activity. Overall, the two fish partition their food resource weakly by consuming prey items in different proportions and sizes and more strongly by utilizing the food resource at different times.
TL;DR: The results indicate that the homing behaviour of Atlantic salmon is not a direct consequence of a single imprinting of the smolts, and that there is not an direct genetic link for return to a particular river, support the sequential imprinting hypothesis proposed by Harden Jones (1968).
Abstract: The dispersal and migration of farmed Atlantic salmon, Salmo salar, allowed to escape during the summer was studied. Three groups of 4–year–old fish of the River Imsa stock were released in coastal waters off south-western Norway: one group, with functional olfactory organs, was released at a fish farm 4 km away from the R. Imsa; two other groups, one with transected olfactory nerves and the other with functional olfactory organs, were released in the sea 90 km from the R. Imsa. To compare them with the migration pattern of reared, large smolts of the Imsa stock, a group of 3 + smolts was released in the R. Imsa.
Adults of salmon released as 3–year–old smolts homed with high precision to the R. Imsa. Four– year–olds released in the sea were recaptured in the fjord and in the coastal current, the majority north of the places of release. Immatures migrated to feeding areas in the North Atlantic. Matures seemed to enter rivers at random when ready to spawn. There was no difference in migration pattern between anosmics and controls. The olfactory sense was not mandatory for entering fresh water. The results indicate that the homing behaviour of Atlantic salmon is not a direct consequence of a single imprinting of the smolts, and that there is not a direct genetic link for return to a particular river. The present results support the sequential imprinting hypothesis proposed by Harden Jones (1968).