摘要:

Abstract.Measurements of egg number, egg size and total egg volume in relation to post‐stripped weight, made on the eggs stripped from 12 separately maintained farm stocks of 4‐year‐old rainbow trout.Oncorhynchus mykissRichardson, revealed highly significant differences between populations when analysed by regression and covariance statistical techniques.All of the stocks showed increases in fecundity with increasing fish size, with 61% (coefficient of determination or r2) of the variation in fecundity of the 12 stocks explained by the common regression on parental fish size. Comparison of the regressions of the different stocks revealed that the rate of increase of fecundity with increasing fish weight was constant throughout the weight range (i.e. the regressions had similar slopes) although there were highly significant differences in elevation, with some stocks producing almost twice as many eggs as some of the others.By contrast, the relationship of egg size with fish weight was much more variable with three of the stocks showing no significant regression of egg size on fish weight and a further two stocks with data poorly fitted to the regressions. Of the remaining seven stocks only one showed a significant difference in slope of the regression with modest increases in fish weight being associated with large increases in egg size. Only four of the remaining stocks of fish showed significant differences in the elevation of their regressions, i.e. the egg sizes were significantly different after the potentially conflicting influence of fish size was partitioned using covariance techniques.Assessments of total egg volume produced far improved regressions on post‐strip weight with 75% (r2) of the variation in the pooled data of the 12 stocks being described by the line of the common regression. In general, there appeared to be a “trade‐off” between egg number and size with the most and least fecund fish producing somewhat smaller and larger eggs respectively. All 12 regressions of totai egg volume on fish weight showed a common slope. However, there were significant differences in elevation of the regressions, with some of the stocks of trout producing up to a 55% greater volume of eggs.There appeared to be no relationship between the differences in egg number, size or total egg volume and the type or geograpfiical location of the farms on which the stocks were held.Although it remains to be determined to what extent these differences in reproductive performance are Inheritable, it is recommended that these characteristics should be taken into account by hatcheries in tbe design of long‐term broodstock selection programmes fo

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00465.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The Chilean oyster,Ostrea chilensisPhilippi, shows high phenotypic variability for growth rate within populations. In order to determine if the serial correlation of growth rate in oysters is positive, the correlation between shell height and live weight at different stages of the life cycle in a cohort of the Chilean oyster was estimated. Four size groups of individually tagged oysters selected on the basis of their shell heights were examined. The relationships for juvenile and adult oysters were found to be positively correlated throughout the study period. The correlation coefficients ranged from r = 0.28 to r = 0.83. For shell height the coefficient of determination for market size oysters was higher in 2‐year‐old (r2=0.88) than in 1‐year‐old oysters (r2=0.09). Shell height and live weight were more highly correlated at later stages of the life cycle. The results indicate that 2‐year‐old oysters have a size that is indicative of performance to market size and hence is an appropriate age to select the parents to be used in breeding programmes to improve the growth rate inO. chilensis. A high mortality was detected after the natural spawning period. A physiological stress hypothesis is proposed to explain the high summer mortality inO. chilensisin the Quempillen estuary, sou

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00466.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The morphometric relationships, standard length‐weight, standard length‐width and weight‐width forCichlasoma urophthalmus(Günther) in the weight range 0.78‐262g were: log10weight =−4.35 + 2.95 × (log10standard length); log10width =−0.73 + 0 99 × (log10Standard length) and log10width = 0.74 + 0.33 × (log10, weight). Two box graders were designed and tested based on these data. The operation efficiency (expressed as a percentage of the sample used to test it) was 96.1 % and 95% for the two graders. Results indicated a tendency to undergrading (small fish detained by the bars) by the first grader and overgrading (large fish going between the bars) by the second, the latter as a result of the major variability in the body shape from fish as they grow. The results are satisfactory, and larger graders for commercial use could be constructed based on thes

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00467.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Triploidy was induced in the zebrafish,Brachydanio rerio(Hamilton), by varying all possible combinations of the time after fertilization (AF) (1‐3min after insemination), temperature (36‐42°C) and shock duration (1‐7min). A thermal shock of 41°C for 4min, 2.5min AF ensured 100% triploidy and maximum (51%) survival. Induction of triploidy was confirmed by measurement of erythrocyte nuclear volume and chromosome counting. There was no significant difference in the growth rate of triploid and diploid fishes. All surviving triploids developed into males, and produced a few spermatozoa unable to fertilize normal eggs. A study on thermal and other characteristics required to ensure 100% triploidy rate in fish indicates that these characteristics are species s

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00468.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Oxytetracycline (OTC) was intraperitoneally injected into pike,Esox luciusL., to determine the validity of ages derived from cleithra and pelvic fin rays, to determine the rate of OTC incorporation into calcified structures, to decermine suitable marking dosages and to assess OTC‐induced mortality.The results showed that annuli were laid down on pike cleithra and pelvic fin rays. OTC was incorporated into most calcified structures as early as 6 h after injection and all structures were marked within 24 h. A dosage range of 25–50 mg OTC/kg fish was appropriate for marking pike. OTC‐induced mortality was statistically insignif

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00469.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The behaviour was compared of juvenile reared and wild cod,Gadus morhuaL., towards a potential predator. The cod were allowed to swim and feed freely in a tank, separated from a predator (large cod) by a transparent Plexiglas wall. The reared cod remained further from the predator than the wild cod, and were slower to approach the predator. The relevance of these findings for extensive rearing of cod is discussed.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00470.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.To assess the merits of rearing coho salmon,Oncorhynchus kisutch(Walbaum), smolts semi‐naturally, trials were made in which 17 groups of tagged smolts, from 4 brood years, were raised on a partially natural diet in a semi‐natural habitat. Their subsequent survival, as determined from catch and escapement, was compared with that of four groups of smolts, from the same brood years, raised by a conventional hatchery method. The returns of the semi‐natural fish proved lower than or similar to those of the hatchery fish, which attained a maximum survival to catch and escapement of 26%. The survival of the semi‐natural fish showed no relation to their location in their linear rearing facility, nor to size of smolt (within a narrow range). Further trials showed that a month's delay in release of the semi‐natural fish did not increase returns, contrary to a current predictive model. The distribution of the catches of both kinds of fish was broadly similar in the troll and sport fisheries. It is concludedthat semi‐natural rearing of coho smolts is not superior to that of standard hatchery procedures, although it may be favoured for specific locations that lend themselves to th

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00471.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Details of mean annual slocking rate and catch of eels in a random sample of 68 Polish lakes over a period of 36 years are presented. Multiple correlation and curvilinear regressions are used to assess the effectiveness of stocking. Maximum stocking rate of 275 elvers/ha/year and maximum catch of 5.2 kg/ha were determined. Yields per recruit were highest in the lakes in which the greatest catches of other fish were made and stocking was most effective in lakes of depth less than 5 m.The theoretical maximum catch of 5.2kg/ha was very much less than maxima observed elsewhere. Two possible contributory factors are the Polish practice of using relatively large‐meshed seines for fishing, permitting the escape of eels of less than 50cm and the relatively small number of potential competing fish species in fisheries such as that of Lough Neagh in Irelan

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00472.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The performance of fyke netting was compared with that of electrofishing in an artificially stocked closed pond and in open waters with natural populations in the Thames catchment, England. Seine netting, trapping and fyke nets of different mesh size were also compared using wild populations. Studies of mark‐recapture and catch‐depletion techniques for estimating population sizes and structures were included. It was concluded that no single technique was ideal because of the difficulties inherent in adequately sampling eels in all aquatic environments. Recommendations are made and the implications of fyke net efficiency for commercial fishing are discus

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00473.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00474.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY