摘要:

Testicular development in the adult maleF1sturgeon hybrid, the bester (Huso husoL. female xAcipenser ruthenusL. male), was examined monthly in relation to serum sex steroid levels. Spermatogenesis lasted for 1 year, with meiosis generally starting in September and spermiogenesis in November, although there was considerable variation in testicular developmental stages between fish sampled monthly. Testicular development continued, slowly, during the winter months until April. Fish did not exhibit spontaneous spermiation, and phagocytotic activity of Sertoli cells became prominent from May onwards. Androgen levels increased during Spermatogenesis and remained high throughout the pre‐spermiation period. In the degeneration stage, 11‐ketotestosterone concentrations declined to low levels, while testoster‐ one levels remained high. The serum concentration of 17,20β‐dihydroxy‐4‐pregnen‐3‐one was low throughout the reproductive cycle. Based on these results, it is suggested that the time appropriate for induction of final maturation would be from November–December to April when the testes are in the late st

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01802.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The nuclear DNA content ofSalmo fibreni, endemic to Lake Posta Fibreno, and of the sympatricSalmo trutta macrostigma, was evaluated using flow cytometric (FCM) analysis. The DNA content was 6‐29 pg/nucleus for male and significantly greater at 6‐41 pg/nucleus for femaleS, fibreni;and 6‐37 pg/nucleus for maleS, trutta macros

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01803.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Von Bertalanffy growth parameters were estimated for silver hakeMerluccius bilineariswithin four regions of the United States continental shelf ecosystem of the northwest Atlantic Ocean during 1975–1980, 1982–1987 and 1988–1992. Differences in silver hake growth were found between the Middle Atlantic and southern Georges Bank regions (P<0–01) over all three time periods. Growth also differed between northern Georges Bank and the Gulf of Maine (P<0–01) during 1975–1980 and 1982–1987, and significant differences between southern Georges Bank and northern Georges Bank were found only during 1982–1987. Silver hake in the Gulf of Maine exhibited larger asymptotic sizes, but attained their asymptotic size at slower rates (L00= 47 cm andK=0–33) in comparison to silver hake in the Middle Atlantic (L00= 43cm andK=0–51), while growth parameter estimates for silver hake on Georges Bank were intermediate between these. Although significant differences in growth of silver hake between the various regions are consistent with separate stocks in the U.S. continental shelf ecosystem, the growth characteristics from the different regions are inconsistent with the presently assigned stock boundaries. (c) 1996 The Fisheries Society

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01804.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Major life history characteristics of daceLeuciscus leuciscusfrom the R. Yenisei at Mirnoye (66° N, Central Siberia, Russia) were determined in June 1993 and were compared with those available throughout the distribution range of the species. Differences between populations located 25° further south and 8000 km away are smaller than those described for other freshwater fishes, whose distributions fall within that of dace. For all the populations, the growth rates (K) are inversely correlated with latitude but these rates for the actual growing season are faster in northern dace. The latitudinal (spatial) variations in the growth rates resemble the temporal variation described for the R. Frome (U.K.). Also, the variations in fecundity between populations are comparable to the temporal variations reported for this British river. Fecundity of the Yenisei dace was correlated with female length [logF=–3–6284+4–0424 x logL] but these females spawned lower numbers of eggs than other populations; and the size of their eggs, like those of the Siberian Ust'Ilim dace, did not vary with female length. We hypothesize that a similar spatio‐temporal response to low water temperature, coupled with limitations of energy for reproduction, may result in a constant egg size in Siberian dace. The effects of other selective forces cannot, however, be

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01805.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

An association between heterozygosity at six to nine enzyme coding loci and correlates of fitness (survival, age at first maturation) was tested in two cohorts of rainbow troutOncorhynchus mykissreared in the laboratory. A subsample offish from the first cohort was reared together for 3 years. There, fish sampled as embryos, juveniles and adults did not differ significantly in multilocus heterozygosity (MLH, numbers of heterozygous loci per fish). However, fish that died during a period of high natural mortality had significantly greater MLH than those sampled before as hatched embryos and later as adults. The number of homozygotes and heterozygotes at three loci differed significantly among different aged fish but in different directions. Allele counts at two of these loci also differed among samples. In a second cohort, the heterozygosity of fish that died during the period of high natural mortality was compared with that of healthy fish collected at the same time; no significant differences in MLH or allele frequencies were detected. Taken together, the lower MLH of the natural mortalities as well as single locus effects observed in the first cohort might be explained by the differential survival of fish with particular genotypes leading to changes in heterozygosity of the entire cohort over time rather than heterozygosityper se. Age of first maturation and heterozygosity (MLH and single locus) were not associated in males but were marginally so in females. Time of ovulation within the spawning season was not associated with the MLH of females.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01806.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

In the Catalan Sea (NW Mediterranean)A. rostratuswas found on the bottom below 500 m and reached its maximum abundance and biomass at 1100–1300 m depth, being captured down to 2209 m. Mean fish size increased progressively with depth. Larger fish were predominantly females, and 50% of maturity was reached at 23–6 and 27–7 cm in males and females, respectively. Although a high percentage of the population was mature all year round, a peak was attained in autumn, coinciding with the slowest growth of the species. Size‐at‐age indicated a slow growth rate. The greatest observed age was 23 years, although most of individuals were 7–12 years old. Overall,A. rostratuscan be considered as a typical K‐strategist, showing a good adaptation to the oligotropic deepse

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01807.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Immature male and female and maturing male Arctic charrSalvelinus alpinuswere held at constant temperature (4° C) under either simulated natural photoperiod (nLD) or constant photoperiod (12:12 LD) conditions, and feed intake and growth were monitored at monthly intervals over 13 months. Food was supplied in excess during a 5‐h period each day, and daily consumption was determined using X‐radiography. Food consumption and growth of both immature and maturing fish showed distinct seasonal cycles irrespective of photoperiod treatment. Feed intake and growth rates were highest in mid‐summer and lowest in autumn. The fact that seasonal cycles persisted under constant photoperiod (12:12 LD) and temperature conditions suggests that circannual rhythms of food consumption and growth exist in the absence of seasonal changes in these environmental cues. The data support the view that seasonal changes in food consumption and growth in the Arctic charr are driven by endogenous rhythms. Reductions in feeding and growth in autumn occurred about 1 month earlier in the maturing males than in the immature fish. Males that matured under the 12:12 LD regime displayed a growth cycle that was delayed in comparison with that shown by the maturing males held und

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01808.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Upper lethal temperature tolerance was determined for 26–81 mm, age 0 black crappiePomoxis nigromaculatusof three size classes using both a rapid transfer and slow heating protocol. Rapid transfer protocols determined 24 LT50values of 33–8, 35–1 and 31–5° C for size classes with mean total lengths of 30–2, 45–6 and 74–9 mm. A predictive model was generated from the slow heating protocols that relates lethal temperature to acclimation temperature, total length, and condition factor (K)

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01809.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Amphiprion ocellarisindividuals were removed from their host anemones on three coral reefs and transferred to a recipient site lacking anemonefish. Return surveys were conducted around 7 days and 330 days after transfer. Survival rates 1 week after transfer were high. The fish surviving 330 days after transfer were those that were shorter. This contrasted with the control fish where survivors had significantly longer initial lengths than non‐survivors. Relative length gain of transferred fish increased with decreasing total length, also contrasting with the control individuals. Percent survival rates were significantly lower in largest transferred fish, relative to the largest control individuals. Relative length gains of transferred fish were highest in the smaller fish contrasting with the growth of the control fis

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01810.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

WeakfishCynoscion regaliswere collected from commercial fisheries in the Chesapeake Bay and the Middle Atlantic Bight (n=4380) during 1989–1992 and their reproductive biology assessed using the gonadosomatic index, macroscopic gonad stages, oocyte diameter distributions, microscopic whole oocyte analysis and histology. Sex ratios were approximately 3:1, females to males, in 1990–1992. Most fish (90%) attained sexual maturity by age 1 and at a small size. Estimated mean length at first maturity was: 164mm total length (TL) for males, and 170 mm TL for females. Weakfish spawn within the Chesapeake Bay, as far north as the Virginia/ Maryland border. Although spawning occurred during May–August and gonad development and initiation of spawning was synchronous, cessation of spawning was asynchronous. There was no indication that older fish exhibited a more extended spawning season than younger fish. Weakfish are multiple spawners with indeterminate fecundity. Oocyte development is asynchronous with oocytes of all stages being present in developed ovaries. Because of the complex and dynamic weakfish ovarian cycle, typical methods of assessing reproduction, such as the GSI and macroscopic gonad stages, are inadequate for this species if not used in conjunction with more detailed methods such as hist

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01811.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY