摘要:

Triloidy was induced in European catfish,Silurus glanisL., by cold‐shocking eggs at 4°C for 30 and 40 min respectively, starting 5 min after fertilization. The hatching success of cold‐shocked eggs was 25–30%. Cold shocks longer than 1 h caused total mortality. The triploid character of the cold‐shocked European catfish was proved by karyological and red blood cell size analyses. The gonads of the triploid fish were significantly smaller than those of the diploids, while the growth rate values of the triploids were significantly higher than those of the

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04968.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The diploid numbers 2n= 48, and 2n= 47 have been determined for the greater amberjack,Seriola dumerili.A chromosome polymorphism due to Robertsonian fusion is present in this species. A simple sex‐determining mechanism has not been observe

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04969.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Elvers were labelled with152Eu and155Eu. Optimum conditions turned out to be incubation for 3 h at 15°C in artificial sea water containing 2% NaCl and 0.1% KCl, EuCl3at 1 mCi (37 MBq) 1−1and an eel concentration of about 15%. Laboratory experiments pointed to a biological half‐life of added europium of 1.6–0.5 years. Thirteen hundred155Eu‐labelled elvers (50 Bq per eel), each weighing on average 0.21 g, were set out near Oskarshamn on the east coast of Sweden in June 1982. Three of these were caught nearby in May 1985 and one was caught in August 1985. They weighed then on average 56 g and showed no significant loss of label other than the physical half‐life (5.1 years). All the radioactivity was found in b

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04970.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Lates niloticusis not native to Lake Victoria but was introduced during or shortly before 1960. It remained relatively uncommon until 1975, when the number in the Nyanza Gulf began to increase impressively, the estimated catch rising over 100‐fold between 1978 and 1982. OriginallyLateswas piscivorous, its diet reflecting the composition of the native fish community. The present investigation has revealed that its diet is now almost entirely comprised ofCaridina nilotica, a small microphagous prawn, and juvenileLates.Native fish species, except for the small pelagicRastrineobola argenteus, are very rarely consumed. This change in diet is a result of the shattering impactLatespredation has had on the native fishes, which have been virtually wiped out. The original community, which was dominated by several hundred haplochromine species and the catfishesClarias mossambicusandBagrus docmacwhich preyed upon them, and included two endemic tilapiine cichlids and 38 species of non‐cichlids, no longer exists. It has been replaced by a community dominated byLateswhich now accounts for well over 80% of the fish biomass in the Nyanza Gulf and very nearly 100% in the study area. The only other species regularly encountered wereOreochromis niloticus, an introduced tilapiine, andRastrineobola argenteus, a native zooplanktiv

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04971.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The only carotenoid detected in newly fertilized eggs of wild Atlantic salmon,Salmo salar, from western Scotland was astaxanthin at a concentration [μg carotenoid g−1wet wt of eggs, mean ±S.D. (number of parental females)] of 6.2±1.2(7) in 1982, 6.4±1.8(20) in 1983, and 7.6 ± 13(6) in 1984. In eggs of farmed Atlantic salmon the only carotenoid detected was canthaxanthin at concentrations which varied significantly between farms depending on the level of synthetic canthaxanthin in the broodstock diet. Thus on two farms using feed with 50 μgg−1, the levels were 11.8 ± 3.4(7) and 12.3 ± 2.9(6), while on two farms using 75μgg−1the levels were 18.7 ± 5.0(9) and 21.2 ± 2.7(21). The levels in eggs of one‐seawinter fish (grilse) did not differ from those of two‐seawinter fish reared on the same farm and diet. During development from newly fertilized egg to fry at the end of yolk‐sac absorption, the quantity of carotenoid present per individual decreased, presumably as a result of metabolism. Despite large differences in quantity present, the quantity so metabolized was fairly constant at 2–4 μg carotenoid g−1original egg weight for eggs from two‐seawinter farmed and wild salmon, except that in eggs from farmed grilse it was 7 μg g−1. In fry from wild eggs, 99.14% of the remaining carotenoid was present in the integument (skin and fins) as astaxanthin, astaxanthin monoester and astaxanthin diester. In fry from farmed salmon eggs, 47 ± 8% of the carotenoid present was found in the unused yolk oil droplets and in the liver, and 37 ± 6% was found in the integument as canthaxanthin and an unidentified metabolite of canthaxanthin. These findings explain visible colour differences between fry from wild parents and fry from canthaxanthin‐fed farmed parents, particularly in the fins, liver and residual oil droplets. The canthaxanthin metabolite was also found, together with canthaxanthin, in the skin of farmed adults fed canthaxanthin. Preliminary tests showed it to be unchanged by saponification but reduced by sodium borohydride. For eggs from the three farms incubated under the same conditions in the same season, percentage mortality both to the eyed stage and between hatching and first feeding varied significantly between farms, but percentage mortality between the eyed stage and hatching did not do so. Results combined from two seasons for eggs from three farms and one wild source showed that egg mortality between fertilization and the eyed stage was not significantly different between wild and farmed salmon, but mortality between the eyed stage and hatching, and between hatching and first feeding, were both significantly higher in farmed salmon than in wild salmon. Such differences could not be explained simply by the large differences in egg carotenoid content, but were almost certainly due to factors such as broodstock nutrition, broodstock management, and st

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04972.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Diets containing 17α‐methyltestosterone (17α‐MT) were fed to milkfish,Chanos chanos, both during the spawning season (experiment 1) and after (experiment 2). The daily dosage of 17α‐MT per kg of body weight was either 25 mg or 12.5 mg in experiment 1, and either 12.5 mg or 6.25 mg in experiment 2. The fish in both experiments were smaller than the minimum mature size previously reported. After 12 weeks of treatment, the treated fish had GSIs that were four times higher than the control fish in both experiments. Histologically, the testes of the control fish had only spermatogonia, in contrast to spermatozoa in the treated fish. However, no male possessed running milt. So 17α‐MT induced spermatogenesis but not spermiation in the immature‐s

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04973.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

A constant population of the colonial‐nesting cichlidOreochromis mossambicus(Peters) was maintained, over a long period, in a large aquarium tank. The larger and more dominant males more often held territories in the more sheltered areas, which were favoured by all males, and which seemed to lead to greater courtship success. The aggressive and reproductive behaviour of adult males was analysed and was, initially, found to be strongly influenced by the fishes' relative sizes. Towards the end of the study period, true size became less important in affecting such behaviour than the initial size, suggesting that there was a persistent effect of previous interactions. The initial and final sizes of males were found to be negatively correlated, suggesting that one cost of territorial reproductive behaviour is reduced growt

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04974.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Protandrous hermaphroditism among deep‐sea fishes is known only within one family, Gonostomatidae, and therein restricted to a few species of two genera,Cyclothone (C. atraria, C. microdon)andGonostoma (G. elongatum, G. gracile). Gonostoma bathyphilum, the deepest dwelling (700–2700 m depth) ofGonostomaspp., is also protandrous and shares withCyclothonespp. an expression of sexual dimorphism manifested by the excessive development of olfactory structures, including the olfactory lobes, in ripe males. Sex‐reversal in ripe males, therefore, involves a regression of these structures. The relationships apparent between sex, maturity and olfactory development, and those between animal size, maturity and depth of occurrence, indicate that whilst protandry is an integral component of the species' reproductive strategy some individuals develop directly as females and that among males (max. size 150 mm S.L.) sex‐reversal is not obligatory. Primary females, together with those derived from prematurely reversing males, may form an early maturing female group, spawning for the first time at about 110–120 mm S.L. Most hermaphrodites were<100 mm S.L., and within the 70–99 mm S.L. size‐range a significant proportion had mature male characters. Since males of this size were all found to be immature, this suggests that these hermaphrodites are derived from a precocious element within the initial male population, and, by virtue of size‐stratification by depth, are responsible for mating with the early‐maturing females. The lack of a marked seasonality in the sexual cycle implies an ever presence of all sexual categories within the population. It is conjectured that sex‐reversal of ripe males is a response to critical population density levels of ripe females and that the smaller, precocious males would be more prone to sex‐reversal than the larger, later‐maturing ones. In some respects protandry inG. bathyphilumis similar to that inG. elongatum.In the latter, however, the reproductive cycle is seasonally linked and sex‐reversal in males is probably obligatory. Even so, critical density levels of ripe females can still be invoked as bei

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04975.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The role of bacteria in the nutrition of silver carp was studied byin‐vitrotests, which confirmed earlier results that the potentially important source of nitrogen in bacteria is not utilized by the fish. Cultures of aerobic and anaerobic bacteria, recovered from a fish pond, were incubated with digestive fluids from the gut contents and from tissues surrounding the alimentary tract (Organ of Leydig) respectively. Growth of aerobic isolates was not affected by the digestive fluids whereas growth of all anaerobes was inhibited. A susceptibility test revealed a bacteriostatic rather than bactericidal effect of the digestive fluid on the bacteria. During 42 h incubation at approximately 20°C of gut fluid, trypsin activity decreased between 14% (in fore‐gut fluid) and 62% (in mid‐gut fluid). The addition of aerobic bacteria (to the mid‐gut fluid) or anaerobic bacteria (to the fore‐gut fluid) did not accelerate the degradation

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04976.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

An improvement in water quality in the estuary of the River Thames in recent years, coupled with the return of adult Atlantic salmon following artificial stocking of the headwaters with parr and of the lower river with smolts, has provided an opportunity to define the dissolved oxygen requirements of adult fish ascending the estuary to reach fresh water. Between July and September 1984 the fish traversed a length of 30 km where the concentration of dissolved oxygen was at its lowest, the 5‐percentile and median values being 1.6–2.6 and 3.5–5.9 mg l−1, respectively, depending upon exact location. Within this zone there was a length of about 20 km in which the minimum at any one time during the period was always less than 5mg l−1and a shorter length of 15 km in which it was always less than 4.7 mg l−1, and it is likely that some fish experienced even lower values during their upstream passage. Over lengths of 1, 10 and 30 km, for example, the 10‐percentiles were 2, 2.2 and 2.8 mg l−1, respectively, the medians were 3.6, 3.8 and 4.3 mg l−1, respectively and the 90‐percentiles were 4.8, 4.9 and 5.3 mg l−, respectively. The water temperature during August, when most of the fish were caught, was never lower than 19°C and there was a length of estuary of at least 20 km

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1986.tb04977.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY