摘要:

Abstract.A habitat suitability index (HSI) model for suspended tray culture of the Pacific oyster,Crassostrea gigasThunberg, was constructed from existing information in the literature on oyster‐environment relationships. In the model, biophysical data are used to rate aquaculture potential of coastal areas on a scale from 0.0 to 1·0. where 1·0 represents optimal conditions for growth and survival and 0·0 represents totally unsuitable habitat conditions. The model was tested with environmental, growth (increase in shell height) and secondary production (g· 100 oysters−1day−1) data collected over a 14‐month period for two age‐classes of oysters transplanted to 10 locations along the coast of British Columbia. Canada. Regressions of HSI values calculated from entire study environmental data against oyster growth and secondary production were highly significant for both age‐classes. Environmental data subsets representing short sampling programmers (1–3 months) resulted in HSI values significantly correlated to oyster growth, provided that some sampling occurred during periods of high food availability. HSI modeling techniques have potential application in site selection and coastal manageme

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00414.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.In continuation of an experiment carried out in 1983, the effect of polyculture of bottom‐feeding fish (common carp.Cyprinus carpioL.; tilapia hybrids,Oreochromis nilolicus(L.) ×O. aureus(Steindadner); and grey mullet,Mugil cephalus(L.) and a filter‐feeding fish (silver carp.Hypopluhalmichtys molitrix(Valenciennes)) on the nannoplankton and netplanklon has been studied. This effect was analysed through principal component analysis. The results confirmed the linding of 1983 that the presence of silver carp in a pond, either alone or with bottom‐feeding fish, results in a decrease in netplankton (phylo‐ and zooplankton) and an increase in nannoplankton which passes through the tiller apparatus of the fish. The effect of the silver carp seems to be related more to its numerical density than to its individual weight, since the effect diminished with the decrease in density during 1983–1985. It became least pronounced when the density was 400/ha. Bottom‐feeding fish enhance the development of the larger nannoplankton by bringing up nutrients from the bottom, but reduce the number of the netplankton (mainly zooplankton) as compared to the control pond without lish. This effect was more apparent at a higher density of tilapia. but was masked when silver carp

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00415.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The influence of temperature on growth of European eels,Anguilla anguillaL., of various body sizes was studied. The mean weight of small eels (SE) (0·6g body weight) maintained at 23°C was significantly lower than that of SE maintained at 25°C or 27°C. No significant differences were found at the end of the experimental period between SE maintained at 25 and 27°C. Similar results were obtained among the moderate‐size eels (ME) (l·5gbody weight). However, the average weight increase maintained at 25°C was significantly higher than that of large eels (LE) (3·25g body weight) maintained at 23 or 27°C. It seems that the optimum growth temperature for European eels is different at various stages in their growth and d

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00416.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Artificially reproduced pacu,Colossoma mitreiBerg, fingerlings (initial weight 41 g) were stocked (100/m3) in plastic cages (1·0m3) within a freshwater reservoir. Three diets containing 30, 35 and 40% protein were tested in quadruplicate over a 76‐day experimental feeding period. Fish were fed 7 days a week, twice daily at a feeding regime of 4% body weight/day from stock to 100g and thereafter at 3% until harvest. Mean water temperature over the trial was 26·7°C. Significant differences were observed in total and daily gain and in protein efficiency ratio, while no differences were obtained in the feed conversion ratio between treatments. Based on this study a 35% protein ration is recommended for pacu within floating c

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00417.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Samples of water, sediment and fish were collected from six commercial channel catfish,Ictalurus punctalus(Rafinesque), ponds from May to October and analysed for muddy‐odour producing compounds. Three episodes of off‐flavour in the fish occurred in late summer. The episodes were of 2–3 months' duration and correlated with the levels of 2‐methylisoborneol in water, sediment and fish.Oscillatoria agardliiiwas the dominant phytoplankton in ponds with off‐flavour fish. Other known muddy odour‐producing compounds such as geosmin, 2‐isopropyl‐3‐mcthoxypyrazinc, 2‐isobutyl‐3‐methoxypyrazine and 2‐isobutyl‐6‐methoxypyrazinc were not detected in the water sediment or at concent

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00418.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Counts were made of cormorants,Phalacrocorax carbo(L.), feeding on the River Bush. County Antrim. Northern Ireland during the post‐dawn period on three occasions. Two of the counts during May 1986 indicated that up to 264 birds may have been feeding at least once per day throughout the catchment during the salmon,Salmo salarL., smolt run. The number of feeding birds had dropped to an estimated 61 by the time of the third count on 1 July 1986. Stomach samples from shot birds showed that upstream feeding was concentrated on wild smolts and brown trout.Salmo truttaL. However, cormorant predalion downstream from the salmon hatchery at Bushmills was restricted solely to hatchery smolts. Estimates of the total daily predation rates were calculated at 653–1214 wild smolts. 107–231 hatchery smolts and 422–785 brown trout. The possible impact of this level of predation on the salmonid stocks of the river was a

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00419.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Larvae and juveniles of two species ofCoregounssp. were immersed in tetracycline (TC) solutions (200–800)mg/1) and fluorescent marks in the otoliths from fish were identified under a UV‐light microscope. Whitefish.Coregonus Iavaretus(L.). juveniles (average weight 191 mg) immersed in TC solution retained their marking until the 127th day, hut 40% of the population lost their TC marking after wintering. Whitefish and peled.C. peledGmelin, larvae retained TC marking from the TC solution (400 mg/1) if water temperature was higher than 5°C, Whitefish juveniles retained clear marking in the otolith after 120 days of post‐immersion rearing. Peled larvae immersed in TC solution were grown in a pond and the fluorescent otolith centre of 55·4‐g fish was well visible after processing. Nearly 100% of peled larvae grown for 176 days can he identified based on fluoresceent marks observed under a UV‐lighl

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00420.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The autccology of chub,Leudscus cephalus(L.), in the Renlina Stream, Greece, was carried out in an effort to obtain information on the age, growth, mortality and reproduction of this species. Fork length increment during the first year of life was 8·9cm, after which it decreased. Life span was short (maximum age 8 years) and the instantaneous mortality rates were higher for the older age‐groups. Chub reached sexual maturity at the second year of life for both sexes and spawning occurred from the second fortnight of April into May, at a mean water temperature of 18°C. The relationship between fecundity (F) and fork length (1) wasF= 0·0797 L3·63The average density and biomass were 1·06 fish.m−2and 11·38g.m−2respectively. The relationship betweenLand the pharyngeal bone size [gape (G), tip (T) and shank (S)] in mm and caudal fin length (C) (cm) can be described by the equations:L= 0·8605 + 1·550G,L= ‐0·0703 + 1·332S, L= 1·092 + 1·615Ta

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00421.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.A variety of liming techniques were investigated to mitigate the effects of long‐term acidification of Loch Dee. a rapid‐turnover loch in south‐west Scotland.Of the limestone chips and powder added to the major inflow stream plus powder added to the catchment between 1980 and 1982, only 3·6% was calculated to have reached the loch and none was lost at the outflow. After the addition of limestone powder to the loch in 1983. via the major inflow stream, the calcium levels increased in the loch but 50% of the added limestone was calculated to have been lost at the loch outflow, Within 2 years, calcium concentrations and pH had relumed to pre‐liming levels. Calcium uptake by sediments accounted for about 28% of the 75 tonnes of limestone added although this was probably n conservative estimate.These results suggest that, in sensitive rapid‐turnover lochs, the addition of limestone will be at least a regular requirement if water quality is lo be maintained at levels desirable for maintaining a viable fishery, A high initial dosage will also be required due lo calcium uptake by

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00422.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The construction of a multiple electrode fishing boom is described. The efficiency of the equipment was compared with more conventional hand‐held electric fishing equipment and seine netting in a series of field trials. Differences were found in the fishing efficiencies of the equipment teslcd. The boom electric fishing equipment with a pulsed direct current output produced better and more consistent catches and is considered to he a good cost‐effective method for sampling large linear water bod

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00423.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY