摘要:

Abstract.For a study of the fecundity ofMacrobrachium rosenbergii, a total of 117 berried females were sampled from ponds. Fecundity was found to vary from 1216 to 89747 eggs for prawns measuring 9.0cm to 15.8cm total length and weighing 6.22 to 45.80g. The relationship between fecundity (EN) and total length (TL) was found to be EN = 0.001876 TL6.3617.The average egg number/g total body weight for prawns having orange, yellow and grey eggs was 1132.7 ± 484.1,766.4 ± 524.3 and 745.5 ± 487.2, respectively, a decrease of 32.3% when orange eggs became yellow and 34.3% when they turned grey. This decrease was probably due to unfertilized eggs dropping off and some eggs being eaten by the brooders during the incubation period.Egg numbers/g egg weight were found to be 11360.1 ± 1642.1,10715.7 ± 2725.3 and 8634.0 ± 1892.3 for orange, yellow and grey eggs, respectively. When compared to orange eggs, yellow eggs were slightly heavier (6%), but grey eggs were significantly heavier by 31.6%. The increase in the weight of the grey eggs can be explained by the elongation of fully formed organs and appendages by about 17 days post fertiliz

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00488.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.This study is based on a description of the anatomical development of live eggs and larval characteristics of queen conch,Strombus gigasL., before hatching, and the development of these characteristics at five different temperatures (24°C, 26°C, 28°C, 30°C and 32°C). The effect of temperature was quantified with reference to six easily identifiable morphological changes, selected from 27 identified characteristics. The relationship between the appearance of the six characteristics and water temperature was used to calculate the minimal biological temperature (MBT) for queen conch. The “degree days” for each characteristic until hatching were determined. These data can be used to predict ihc hatching time at predetermined temperatures in culture systems. The work also has the benefit of providing synchronously developed material for S. gigas for developmental, biological, physiological and biochemical research of this

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00489.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The effectiveness of xylocaine anaesthesia, potentiated with sodium bicarbonate, was investigated on the altiplano cyprinid,Algansea lacustrisSteindachner. The drug gave excellent sedation, handling and recovery and was effective at doses between 50 and 300 mg/l in 1 g/l sodium bicarbonate.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00490.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.At different temperatures (4.5, 6.0, 8.6, 10.4, 13.5, 15.9 and 19.0°C), time from hatching to exogenous feeding (DEP50) in vendace,Coregonus albula(L.), larvae decreased from 8 to 2 days when the temperature increased from 4‐5 to 19 0°C. Starved larvae at 10.4°C, when offered food at successive days after acclimation to different temperatures, started external feeding on the same day, irrespective of the acclimation temperature.Larvae started exogenous feeding after attaining a particular larval development stage (LDS 1‐2), while their age (days after hatching) was of secondary significance. In the vendace population the larvae start exogenous (mixed) feeding at a total length of 9.5 mm, irrespective of their age and rearing temperature. As total length of larvae is closely related to their development stage, the length of fish can be used in a hatchery practice as a parameter indicative of the time of the first feeding of larvae or of their release into the stocked

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00491.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The effect of different levels of organic enrichment on benthic productivity was studied over a 16‐week period in trays of sediment placed in a fertilized seawater pond. Primary and secondary planktonic production were also monitored. The exploitation of these sources of food by juvenile sole and their growth and survival over an 8‐week period were assessed.The colonization of the sediments showed a marked succession. Nematodes were numerically the most abundant group and reached a peak after about 8 weeks. This was followed by a peak in the abundance of epibenthic copepods after 11 weeks. The maximum numbers of poiychaetes and larger Crustacea (mainly amphipods) occurred at the end of the trial (15 weeks). The high‐organic sediment supported fewer polychaetes and copepods than either the low‐ or medium‐organic sediments. The species composition of the benthos varied both with the level of organic enrichment and with time. Peaks of zooplankton concentrations of 23 to 25 organisms/l occurred during the spring and late summer. There was some evidence of an inverse relationship between zooplankton abundance and standing crop of algae, as indicated by chlorophyll a concentrations.Harpacticoid copepods were the dominant food item consumed by small (21‐50mm total length) sole. Polychaetes, amphipods and Crangon spp. were exploited by large (61‐90mm total length) sole to a much greater extent, though harpacticoid copepods were also commonly taken.The percentage increase in length of the juvenile sole at low‐, medium‐ and high‐organic levels was 108, 146 and 152 respectively. Survival, however, was highest (100%) on the untreated sediment and lowest (57%) at the m

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00492.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The feasibility of using a smalt nutrient‐film hydroponic technique hydroponics unit as a mineral filter for a recirculating aquarium system has been Investigated. The aquarium in question employed microbial biofilters to convert ammonia and waste materials to a mineralized form, particularly nitrates.A recirculating NFT system was designed using a 40‐l capacity catchment refilled at weekly intervals from the aquarium, which was stocked with common carp,Cyprinus carpioL. and rainbow trout,Oncorhynchus mykiss(Walbaum). Four crop species were grown (garden peas,Pisum sativumL., lettuce,Lactuca sativaL., watercress.Nasturtium officinaleR., and barley,Hordeum vulgareL.) with no additional nutrient supply. A control system was set up using tap water. Although yields were not as high as seen in commercial NFT systems the aquarium water‐fed system produced viable plants, with higher yields and better quality than seen in the controls. At the same time mineral levels, especially nitrates, were reduced.If the unit was incorporated into the aquarium filter system as a single passage unit, water quality could be maintained, together with the production of a useful crop. The data obtained in the present study are compared with previous reports on the use of hydroponics in conjunction with fish cu

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00493.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.In four experiments, performed at the Agricultural University, Wageningen and the Netherlands Institute for Fishery Investigations, the effects of attractants on feed acceptance and growth of glass eels, Anguilla anguilla L., were studied. The results show that extracts from natural food or a mixture of synthetic amino acids improve acceptance of a trout fry crumble at first feeding of glass eels. Overall results can be greatly improved by initiating the feeding behaviour of the fish by feeding cod roe for the first few days. The results also demonstrate a strong effect of the feeding level on feed acceptance. At relatively high feeding levels no significant effect of attractants could be detected.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00494.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.World production and consumption of eels, Anguilla spp., was about 100000‐110000 tonnes/year in 1987. About 70‐80% of the world production is consumed in Japan. This amount is almost completely produced by eel culture in Japan and Taiwan. The remaining 20‐30% of the world production is consumed in Europe. About 15% of Ihe European eel market, i.e. 3000‐4000 tonnes/year, is covered by cultured eels.In this review a description is given of the history and present status of eel culture in Japan and Europe. The economical comparison between eel culture in Japan and Europe shows much higher levels of both production costs and sales prices in Japan. Uncertainty about the future price developments and competition within Japan and with Taiwan (and China) keep a constant pressure on Japanese eel farmers to optimize their production process. Although a further optimization of the recirculation systems in north‐west Europe is also needed, it will depend on the availability of trained husbandry personnel and on the future development of the eel market in Europe whether eel culture in north‐west Europe can in the long term remain competitive with natural catches and with eel culture in the Mediter

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00495.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The reservoir fishery of China is essentially a post‐1950 development. China has an estimated reservoir acreage of 2 × 106ha of which about 1.44 × 1O6ha is used for fisheries. The present reservoir fish production averages 214kg/ha/year and accounts for about 8‐9% of the total inland fish production, which is around 4.0 × 1O6mt. The total reservoir fish production and production per unit area in China have been steadily increasing since 1980.The Cwhinese reservoir fishery is essentially a stock and capture fishery. The reservoir management practices and aspects of the present fishery are discussed. Those practices which are not found in the rest of Asia are highl

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00496.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The pre‐acidification level of Atlantic salmon,Salmo salarL., production in Norway was estimated from accessible rearing habitat, potential smolt production, smolt to adult survival, and mean adult weight. Atlantic salmon have been virtually lost in 25 rivers due to acidification. In total, 340.6km of river is affected, and this corresponds to a rearing area of 2044.8 ha. The total annual number of adult salmon lost was estimated to be between 92016 and 306720 individuals, weighing some 345‐1150 ton

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00497.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY