摘要:

Abstract.The objective of this study is to determine the optimal protein level for best growth and development ofRana pereziSeoane larvae. Performance of four diets containing 28%, 33·5%, 39% and 45·5% protein was compared. Tadpoles provided diets with 39% and 45·5% gross protein achieved the best results with regard to growth (weight gain, growth rate, feed conversion, etc.) and development (length of larval period, percentage of metamorphosis, etc.). Considering that protein is the most expensive diet component, it is estimated that the optimum quantity of protein forR. perezilarvae is about 3

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00550.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.Within the framework of a fisheries project in north‐east Thailand, project MK/FSPC/069 entitled ‘The Fish Seed Production Centre, North East Thailand’, an assessment was carried out of the ecological impact of introducing exotic fish species (common carp,Cyprinus carpioL., Nile tilapia,Oreochromis niloticus(L.), and Chinese and Indian carps). For the assessment, the protocol of Kohler&Stanley (1984) was followed, covering feasibility of introduction, acclimatization potential, potential impact, and control potentials. Regarding the (ongoing) use of the proposed exotic species in aquaculture, it was concluded that so far no clear ecological impact has been reported from escapes to open water; the use of the exotic species has shown to be highly beneficial from a 9 socio‐economic point of view. Regarding the proposed introduction of the exotic species into public waters (natural lakes and man‐made reservoirs), it was concluded that earlier releases of these species in north‐east Thailand did not provoke severe ecological impact in terms of deterioration of aquatic ecosystems. Incidental cases of minor ecological impact were reported for common carp and nile tilapia. Indications were obtained for niche competition between Chinese and Indian carps and indigenous carps, while similar niche competition was concluded for bighead carp,Aristichthys nobilis(Richardson), and indigenous pelagic zooplankton feeders. Observing the prolific development of the Nile tilapia in a number of reported cases, it was recommended not to include this species in stocking programmes for public water bodies, until more risk assessments ar

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00551.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.In northern Europe, rearing of rainbow trout,Oncorhynchus mykiss(Walbaum), in sea cages is a substantial part of fish culture. One of the major constraints for the development of this system in other parts of Europe is the unexplained mortality of fish during the summer. To investigate environmental aspects of this mortality, rainbow trout, cultured in cages in sea water, were monitored from May to October for three successive years. No evidence of bacterial involvement could be found, while water temperature and salinity strongly influence the mortality. This supports the suggestion that the mortality has been caused by patho‐physiological changes due to higher metabolic requirements for osmoregulation at elevated water temperature in the saline environment which might result in a dissipation of O2by CO2on the hemoglobi

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00552.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.A quantitative gonadal index was developed for oysters,Crassostrea virginica(Gmelin. 1791), using polyclonal antibodies from eggs and sperm. Percoll used in the purification of oyster eggs and sperm greatly improved the purity of antigens compared to filtering the egg or sperm through a fine mesh only. The antigen‐antibody reaction was tested with indirect sandwich ELISA using alkaline phosphatase‐conjugated goat anti‐rabbit igG as a secondary antibody. Rabbit anti‐oyster egg IgG and anti‐oyster sperm IgG initially exhibited a weak cross‐reactivity over somatic tissue. Absoring with acetone‐dried oyster tissue powder removed this cross‐reactivity. Both antisera exhibited strong specific immunological reactions to oyster eggs or sperm respectively. The quantity of eggs or sperm was measured using ELISA and a quantitative gonadosomatic index (dry wt of egg or sperm/dry wt oyster) (GSI) calculated. GSI from ELISA correlated with gonadal stage measured histologically. Monthly mean GSI of female oysters was highest during late spring to early summer (0·157–0·201) and lowest during early winter to early spring (0·002‐0·000). Maximum GSI observed during the study was 0·422 for female oysters and 0·446 for male oysters. Female oysters produce 3·7–65·4 million eggs, with an average of 21·1 million during each spawning. A positive correlation was observed between the number of eggs produced and oyster size; the number of eggs in the gonad increased as oyster size (i.e. total dry wt) increased (r= 0·67); however, the relationship was non‐linear. Large oysters contained proportionally fewer eggs. Prevalence ofPerkinsus marinusparasitism was high, 90–100%, during the study, as was weighted incidence, 1·33 to 2·67, No statistically significant correlation was observed between infection intensity and the per cen

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00553.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.During the years of 1989 and 1990, the yield of the commercial fishery for the catarina scallop,Argopecten circularis(Sowerby, 1835), in Magdalena Bay, was 750 million organisms (5186t of muscles), which were gathered by diving at 12–30m depth. This production is the largest registered to date and accounted for 53% of the total Mexican scallop production since 1981. The formation of large beds in that area is a sporadic phenomenon which needs to be studied. In the present paper, a model to explain the formation of such beds is drawn, in which the bentho‐pelagic red crab,Pleuroncodes planipes(Stimpson, 1860), plays a role as primary substrate for the recruitment of the spat and simultaneously is the active transporter of juveniles into the Bay during the winter months of cold years. Apparently exploitable beds are formed only when temperatures of 16°C or lower, are registered deep inside the Bay for at least 2 months. Relating these findings with short and long‐term temperature fluctuations, it seems possible to predict future exploitable stocks in th

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00554.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.Genetic divergence and phylogenetic relationships amongParastromateus niger(Bloch),Pampus argenteus(Euphrasen) andPampus chinensis(Euphrasen) were investigated by examining the electrophoretic patterns of nine enzymes and sarcoplasmic proteins. Among the 16 loci detected, four were polymorphic inP. nigerand seven inP. argenteus.The allele frequencies of 16 loci were estimated to calculate the genetic distances (D). The averageDvalue among the species increased in proportion to the level of taxonomic category. The relationship estimated by genetic markers accorded well with that estimated from anatomical characters. The three species were clearly divided into two distinct groups at a D value of 6·51

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00555.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.A study to develop techniques for assigning cultured silver perch,Bidyanus bidyanus(Mitchell), to their hatchery of origin was conducted using scale growth patterns. Automated video digitizing equipment was used to acquire circuli spacing information. Discriminant function analyses were then used to classify pond‐raised fish to their hatchery of origin with up to 91% accuracy. One batch of fish was raised under controlled conditions indoors in a tank to manipulate formation of scale growth patterns. When compared with pond‐raised fish, separation was up to 99% accurate. This technique offers scope [or efficient batch marking of pre‐stocked fish, thereby improving the ability of managers to evaluate stocking progr

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00556.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.The food of brown trout,Salmo truttaL., and rainbow trout,Oncorhynchus mykiss(Walbaum). in a small stillwater put‐and‐take fishery in Surrey, England was examined by stomach content analysis of fish caught by angling between the months of April and September 1985. Overall, brown and rainbow trout tended to utilize different food sources. Mann‐WhitneyU‐tests showed most major food items to be eaten in significantly different amounts, the most important exceptions being chironomid pupae and adult Diptera. In all months except April, rainbow trout utilized mainly midwater food, particularly Cladocera. Brown trout fed mainly on benthic food organisms and fish. Spearman rank correlations showed diets to be dissimilar during this period, with significant negative correlations in May and August. These results indicate an absence of interspecific competition for food, and imply spatial separation of brown and rainbow trout. In April both brown and rainbow trout fed extensively on the temporary bottom fauna, mainly trichopteran and megalopteran larvae, and diets were significantly positively cor

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00557.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractWe examined the relationships between fresh and preserved measurements of length and dry weight for larval walleye,Stizostedion vitreum(Mitchill), subjected to freezing and preservation in formalin. Length reductions for both preservation techniques were<5% and decreased with larval size. Dry weight losses ranged from 32·1 to 54·0% for frozen larvae and from 18·2 to 30·1% for larvae preserved in formalin with larger larvae losing proportionately less weight. Freezing caused significantly greater length shrinkage and dry weight loss than preservation in forma

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00558.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00559.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY