摘要:

AbstractThe androgenic and anabolic potential of fluoxymesterone (FM) was evaluated by incorporating the hormone into the feed of Nile tilapia,Oreochromis niloticus(L.) fry. Phenotypic all‐male populations were produced when FM was given at 1, 5 and 25mg/kg of feed. Fry fed methyltestosterone (MT) at 60 mg/kg of feed and 0‐2 mg of FM per kg of feed had a sex ratio of 97‐7% and 87‐3% phenotypic males.No positive anabolic effect was evident in response to adding FM or MT to the feed at the end of the 28‐day treatment period or after an additional 6 weeks of growth without hormone. Growth was less for fry which received 25 mg/kg of FM compared to those receiving lesser rates of FM, 60 mg/kg MT, and

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00784.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractGrowth, mortality, moulting rate and cheliped loss were examined in aquaculture experiments with noble crayfish,Astacus astacusL., juveniles from four different Norwegian populations in the period September 1987‐June 1988. The juveniles were hatched indoors in May 1987 from parents wild‐caught in 1986. The experiments were performed at 18‐19°C in communal rearing units. Mean total length at experiment start was about 20mm in all groups.There were no significant differences in mean size (final mean total length: 32‐2‐34‐8mm). mortality (83a‐900%) or cheliped loss (429‐700%) among juveniles from the different populations when exposed to similar conditions (food: dry pellets; photoperiod: L:D = 8:16). Among crayfish fed fish and potatoes in addition to dry pellets, and with continuous light conditions, mortality was reduced significantly to about 70%. Continuous light conditions significantly increased mean size (final mean length: 36‐1‐389mm).Moulting occurred from November throughout the experiment period. Moulting rate was positively correlated to mortality and growth rate (i.e. mean length increase). A positive correlation between mortality and cheliped loss, along with direct observations of cannibalism, indicated that agonistic behaviour and cannibalism were the dominating mortality factors. It is suggested that continuous light conditions reduce agonistic behaviour and thereb

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00785.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractOne of the main obstacles toward the intensification of aquaculture systems is the accumulation of inorganic nitrogen in the water, A solution demonstrated in this work is to control inorganic nitrogen levels through the induction of microbial protein synthesis. This is achieved by adding a carbonaceous substrate, adjusted in a way so as to supply the needed carbon to immobilize all the non‐utilized nitrogen. Inorganic nitrogen levels are reduced due to the resulting production of microbial protein. The insituproduced microbial protein is a substitute to the protein added with the feed. Fish growth in the treated ponds was higher than the growth in conventionally fed ponds. Protein utilization was doubled due to the recycling of nitrogen in the pond system, leading to diminution of the deleterious inorganic nitrogen accumulation. The price of feed was reduced to 50‐67% of that common in conventional ponds, due both to replacement of protein and limited wash‐out of

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00786.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effect of four seasonally changing and two static light photoperiod regimes was investigated in two populations of rainbow trout,Oncorhynchus mykiss shasta and kamloops(Walbaum), kept under almost constant temperature, diet and management from 1981 to 1990 in Epirus, north‐west Greece (39,40′N, 20,51′E). We studied how different populations (determined according to the different spawning time) responded to the same artificial photocycles and how age influences that process (underyearling, 1 +, 2+ years old). Early sexual maturation with a 2 to 11‐week acceleration of the peak spawning time occurred in fish kept under protocol P1('long’spring days followed by light reduction during autumn).‘Long’days exposure of fish (≥14h light/day) from June (P3) or September (P4) had little (4 weeks) or no effect respectively in advancing spawning time. Trout kept under a‘reverse’(P2) photocycle attained the peak spawning time 4‐9 weeks later than the controls. An 18‐week delay in spawning time occurred in fish kept under P2from the fry stage. Static light regime P5(20 L:4 D to 15 May, then 4L:20D) advanced peak spawning by 6 weeks, while P6(4L:20D from March to August then 20L:4D) delayed spawning by 2‐4 weeks. Photoperiod also influenced the duration of spawning: the Pi protocol increased by spawning spread three times, while P2decreased it (time between the spawning of the first and last fish was 9‐12 days).No significant difference was observed in the percentage of mature females between tested and control groups, except of kamloops fish kept under P1(higher than control, P<0‐01), P2(lower than control, P<0‐05) for their second reproductive cycle. A higher percentage of early mature males occurred under protocol P2. Fecundity expressed as number of ova/kg of fish weight was similar between tested and control groups. Absolute fecundity (total number of ova/female) was lower in trout kept under the‘reverse’P2regime (P<0‐05). No statistical difference was found in egg diameter and weight. Hatching percentage of fertilized eggs was similar between test

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00787.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractCultivation of the macroalgaHypnea musciformis(Wulfen) Lamouroux was conducted from April 1987 to January 1988 at Praia do Forte (State of Bahia, Brazil), utilizing floating racks, Biomass, reproductive state, carrageenan yield and viscosity of algae artificially grownin situwere compared with those from natural populations. Temperature, salinity, pH, dissolved oxygen, organic and inorganic suspended matter and phosphate in surface waters were similar in all experimental phases. Algae growing on the racks exhibited significantly higher daily biomass increase (0·94‐9·69g/m2day dw) than plants from natural reefs (1·39‐1·74g/m2/day dw). Cultivated algae presented a dominance of tetrasporic stages, while algae from the reefs had a high occurrence of vegetative stages. Both cultivated and natural plants showed higher numbers of cystocarpic specimens during the summer. Carrageenan yield of cultivated plants was significantly higher than those growing under natural conditions only during summer‐time experiments, presenting values of 3972% and 38‐28% for experiments and a range of 22·7‐34·88% for the reef plants. However, carrageenan viscosity of cultivated algae was always higher (40·33 ± 4·62 centipoise) and less variable than that found for the reef growing algae (35·71

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00788.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA simple, fast and accurate method for making multicomponent analyses of fish meat using mid‐infrared (IR) absorption technique is presented. Basically, the method involves dissolving fish meat in an alkaline detergent with a blender, forming a suspension that can be analysed with commercial milk infrared analysers. Various types and concentrations of detergents and two blending times were evaluated.The relative repeatabilities, expressed as the residual standard deviation in relation to the corresponding means, of the method were less than 0‐5%, and relative accuracies were less than 2% for fat and total solids and less than 1% for protein. Possible ways to improve the method further are discus

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00789.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractData are presented on the current geographic distribution of Atlantic salmon, Salmo salar L., in freshwater bodies of Europe. They dwell in 14 hydrological systems, including basins of U lakes and three rivers. Nine of the lakes (Ladoga, Onega, Kuito and others) arc located in Russia, one in Finland (Saimaa) and one in Sweden (Vänern). All the rivers inhabited by freshwater salmon flow within Norwegian borders. Most of the lakes and rivers have good connection with the Baltic, White or Norwegian Seas. Over the past 20 years the freshwater salmon stock in Lake Imandra (the Kola Peninsula) has completely disappeared as a result of heavy human impact. The situation with such non‐migratory salmon, which used to be important to fishing and trade, is also critical in all other water bodies. It is necessary, therefore, to elaborate effective measures for protecting and restoring freshwater salmon in the lakes and rivers of Euro

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00790.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractDuring 1985‐88, a total of 17500 under‐yearling (0+) brown trout. salmo trutta L., were released in Låktabäcken Creek in Swedish Lapland. Of these, 15500 had been reared in a pond adjacent to the creek during their first summer, where they fed on natural prey. The other 2000 were conventionally reared hatchery fish fed dry food pellets. All fish were released in the autumn (size 6O‐70mm) at the confluence of the pond outlet and the creek. Electrofishing revealed that the stocked fish gradually spread downstream from the point of release at the expense of the resident wild trout population. In 1989, stocked fish accounted for 70‐90% and 30‐50% of the trout population in the upper and lower stretches of the creek respectively. No long‐term changes in total trout densities or standing crop occurred as a result of stocking. First‐year survival of fish released in the creek varied between 15 and 30% over the 4 years. After 3 years, 5% of the stocked fish remained in the creek. Planted fish grew less rapidly than wild fish during the first year in the creek. Pond fish had a higher survival rate than hatchery fish and showed a greater propensity to disperse from the p

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00791.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe River Soya, Norway, was canalized for agricultural purposes. In order to compensate for damage to the Atlantic salmon,salmo salar L.and brown trout,Salmo truttaL. populations, different weirs were built. The aims of this study were firstly to analyse the effects of weirs covering the river bank and entire river bottom with blasted stones and secondly, to analyse the effects of sediments transported by freshets on the downstream salmon and trout populations after canalization. Restoration of the river bottom with blasted stones provided salmon with more substrate spaces. Densities of trout increased after the river bank was covered with stones. Sediments transported downstream from the canalized river stretch decreased the densities of juvenile salmon and trout.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00792.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractAdvantage was taken of 490 questionnaires completed by anglers to study the effectiveness of ground‐baiting and its effect on nutrient (phosphorus and nitrogen) budgets in 37 water bodies. There was a strict relationship between daily amounts of baits used and daily catch of sixcyprinid species. However, fish catch increased only to a bait rate of about 2 kg/day. Higher amounts resulted in lower catches.Calculations were also made of daily loads of phosphorus and nitrogen introduced by the‘average’angler into a water body, as well as of the amount of nutrients removed by this angler from the aquatic environment with the fish catch. It was shown that although ground‐baiting represented an important source of nutrient input into the environment, using this method anglers removed 22 times more phosphorus and 17 times more nitrogen from the environment (with their catch) than they introduced into it. Turawa Reservoir was used as an example, showing that in Polish conditions, angling may have a beneficial effect on nutrient budgets of such water

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00793.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY