摘要:

Growth, body composition and feed utilization were evaluated for Arctic charr fed a control diet and nine practical diets formulated to contain three protein levels (34, 44 or 54%) at each of three lipid levels (10, 15 or 20%). Fish were raised for 24 weeks at 12° C. Increasing either dietary protein and/or lipid resulted in improved weight gain, feed efficiency and energy retained. Protein efficiency ratio and protein retained were directly related to dietary lipid and inversely related to dietary protein. A sparing effect of lipid on protein was evident where, at each protein level, Arctic charr utilized protein more efficiently with each increase in dietary lipid. Levels of 34% protein and/or 10% lipid were well below the requirements for Arctic charr (initial weight, 4.6 g). Within the range tested, the dietary combination of 54% protein with 20% lipid maximized weight gain and feed efficiency and resulted in fish with low liver and body lipid contents. However, if lowest feed cost per kg gain is an important factor, the 44% protein—20% lipid diet would be less expensive to use, although it results in a minor reduction in growth potenti

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04933.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Changes in the structure of the gonad, skin, interrenal, liver, kidney, stomach, gill and pituitary gland, as well as blood cortisol and haematocrit values were investigated in adult pink salmon during their migration through the Fraser and Thompson Rivers to the spawning grounds. At the commencement of their freshwater migration the gonads of both males and females were in an advanced state of development, the pituitary contained a large complement of well‐granulated gonadotrops, and hypertrophy was evident in the interrenal tissue and in the epidermis of the skin. At this time, no change from the normal sexually immature salmon was evident in the structure of the gill, liver or stomach. Sclerosis of the glomeruli was noted in the kidney. The plasma cortisol level was consistent with concentrations in unstressed salmon.Migration of the fish through a turbulent section of the Fraser River evoked a marked increase in both blood cortisol concentration and in interrenal nuclear diameters.On arrival at the spawning grounds, 10–15 days after entry into fresh water, a general but not marked deterioration of the tissues was evident. The results are discussed in relation to the spawning migration of other species of Pacific sal

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04934.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The hormones 17β‐estradiol, 17α‐hydroxy‐20β‐dihydroprogesterone(17α, 20β‐P), 11‐ketotestosterone, testosterone, gonadotropin and also vitellogenin, were determined during the spawning migration of wild pink salmon in the Fraser and Thompson Rivers in British Columbia. This stock of pink salmon takes approximately 2 weeks to migrate the 333 km upstream to the spawning grounds. Both sexes were at an advanced stage of sexual development when they entered fresh water. In females both the 17β‐estradiol and vitellogenin levels fell precipitously during the migration, to be very low at spawning, whereas the 17α,20β‐P level rose rapidly, to be highest at arrival on the spawning grounds. The gonadotropin level also rose rapidly during the migration, and was highest in spent fish. Testosterone was at a high level throughout, although this level decreased steadily during migration. In many respects similar endocrine changes were observed in the male. For example, in the case of androgen levels, both testosterone and 11‐ketotestosterone fell steadily during migration but were still relatively high at spawning, whereas both gonadotropin and 17α, 20β‐P levels rose markedly as migration progress. However, although the qualitative changes were often similar between the sexes, the levels of 17α, 20β‐P, testosterone, and gonadotropin were considerably higher throughout in females than in males. It is concluded that this stock of pink salmon is at an advanced stage of sexual development when it enters fresh water. The endocrine changes observed during this study represent those controlling the final stages of reproduction, specifically final oocyte maturation and ovulation in females, and the final stages of spermat

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04935.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Juvenile thick‐lipped grey mullet,Chelon labrosus, believed to be about 6–7 months old, possessed well developed lymphoid organs including a clearly differentiated thymus with distinct cortical and medullary zones. However, unlike older fish, the juvenile mullet usually failed to produce antibody in response to a single injection of classical thymus‐dependent antigen (using the soluble proteins human gamma globulin or keyhole limpet haemocyanin). Prior priming of the juvenile fish with antigen was found to potentiate antibody production following challenge with a second dose of the antigen in adjuvant, priming by oral administration being equally as effective as priming by injection. Neither juvenile nor adult mullet produced any significant level of antibody against ovalbumin.The results suggest that, despite their apparently well differentiated lymphoid organs, juvenile mullet still show a certain level of immaturity in their antibody responses to soluble proteins; also that immunization can improve their ability to re

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04936.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Rainbow trout,Salmo gairdneri, cannulated in the dorsal aorta, were exposed to 2 mgl−1aluminium (added as Al2(SO4)3, 18H2O) at pH = 5.0 in hard water of very high calcium concentrations (3.3 mmol 1−1). No changes were observed in the concentration of the major plasma ions. The fish, however, became hypoxic, as seen from a fall in the dorsal aortic oxygen tension from around 100 mmHg to 30–40 mmHg, and a simultaneous increase in carbon dioxide tension. Moreover, exposure resulted in a 15% increase in standard oxygen uptake. The ventilation frequency doubled and swelling of the erythrocytes was observed. The results are discussed in the light of some earlier data on the effects of acid/aluminium exposure in water of low calcium concentration, and reveal an important role for calcium in the physiological responses to low pH and alum

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04937.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The relative effects of inter‐ and intra‐specific competition on the distribution of stocked salmon in relation to depth and gradient were investigated in an upland stream during two summer sampling periods. The stream was divided into two areas by an impassable fish barrier, and trout were removed from the upstream section prior to 2 years of salmon stocking. A small amount of trout re‐immigration to the cleared area occurred. Under sympatric conditions in the downstream section the fry of both species were significantly more abundant in shallow water, whereas the yearling and older fish tended to inhabit the deeper, slow‐flowing areas. Under near allopatric conditions in the cleared section salmon fry changed their distribution to include deeper areas, with shallow, fast‐flowing water becoming the least preferred habitat. This trend for a wide distribution of salmon fry over all the available habitat in the upstream section was maintained in the second year when parr were present but trout remained at very low densities. It was therefore concluded that high inter‐specific competition from trout was responsible for restricting the distribution of salmon fry to shallow habitat in the control area. Intra‐specific competition from older salmon apparently only affected the growth and survival of salmon fry. The regulating mechanisms involved in these inter‐ and intra‐specific effects are discussed in terms of competition for stream resources and predation. Recommendations based on the findings are made for stocking and habitat management o

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04938.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The parasite faunas of 12 species of freshwater fish from 17 localities on the island of Jersey were examined. Comparison of the species composition, number, diversity and equitability of the parasite fauna of each species of fish in each locality revealed that community diversity was always low, that most communities were dominated by a single species of parasite, and that community similarity between host species, and often between sites, was generally low. This was not related to unavailability or distribution of potential, invertebrate, intermediate host species, but appeared to be due to chance colonization events. With two exceptions, little exchange of parasites took place between host species, despite vacant niches in the parasite communities and the absence of competitors, and normal parasite specificity was maintained. Comparison of the parasite communities with those on other oceanic islands suggests that they are poorer than would be predicted by island biogeographical theory, and that this is not a very good predictor of parasite community richness on oceanic islands.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04939.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Clones of the unisexual fishPoecilia formosa, the Amazon molly, live in the wild in association with their progenitor bisexual species, and compete with them for resources. These resources include food, space and also mates, since the Amazon molly reproduces gynogenetically, a process in which sperm transferred from a male host species activates their eggs. Earlier studies of the adaptive mechanisms that facilitate the coexistence of the bisexual and unisexual forms have focused upon male behaviour, but recent work with another unisexual species,Poeciliopsis, demonstrated that female aggressive behaviour may play an important part in determining the ecological standing of a clone.We have extended our observations to female mating behaviour in two clones in the Amazon molly; clone 1 that does not thrive well under laboratory culture; and clone 2 that is hardy and survives very well. There was no aggression between the clones, nor did the clones show aggression towards females of the bisexual species. However, clone 1 consistently was more successful in the number of mating encounters made with the male; it approached the male more often than clone 2 and fled from the male less often. Males also showed some preference for mating with clone 1 females. If there are physiological differences in the wild clones similar to those seen in the laboratory, the mating advantage of the less robust clone 1 may ensure its continued survival in competition with a more vigorous clone.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04940.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Over the 6 years 1980–85, 212 Norwegian rivers have been examined for occurrence ofGyrodactylus salaris:it was found in 26 rivers and six salmon hatcheries scattered throughout the country from Troms county in the north to Sogn og Fjordane in western Norway. The distribution ofG. salarisis connected with the stocking of fish from infected salmon hatcheries. The populations of salmon parr have been drastically reduced in the infected rivers. In later years catches of ascending salmon in these rivers have also sharply declined: in 1984 salmon fishery losses were estimated at 250–500 t.Gyrodactylus salarisis most probably a recent introduction to Norwegian rivers. A primary aim is to exterminate this parasite from all infected rivers and hatcheries: so far this has been accomplished in one river and one hatch

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04941.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Tilapia aureamuscle and liver adenylate nucleotides, the adenylate energy charge (EC), plasma glucose, cortisol and chloride were monitored during acute and chronic temperature stress. Muscle EC is unaffected during acute cold water exposure but decreases significantly when tilapia are exposed to chronic, sublethal, low temperature stress. The decrease in EC is primarily the result of a decrease in ATP concentration. Plasma glucose and cortisol increase when tilapia are exposed to 11–12° C for 60 min, 11 days, and a 5‐week period. Incomplete compensation is evident in 5‐week acclimated fish since glucose and cortisol levels are intermediate between controls and acutely stressed fish. Acclimation to 35° C does not significantly affect plasma glucose and cortisol compared to controls (22° C). Plasma chloride is relatively unaffected by acute and chronic temperature stress. Liver adenylates are not significantly affected when tilapia are subjected to a sudden drop in water temperature (22° down to 11° C). EC is a useful indicator of chronic low temperature stress inT. aurea, while plasma glucose and cortisol are sensitive to both acute and chronic temperat

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04942.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY