摘要:

Abstract.Fry ofCichlasoma urophthalmus(Günther) weighing 160‐175 mg were fed for 75 days on diets containing seven different levels of calcium pantothenate. Fish fed on the three lowest inclusion levels (up to 0,10 and 20 mg/kg) exhibited a variety of external signs and high mortalities. Fish fed on the higher inclusion levels (40, 60, 80, 120 and 320 mg/kg) did not show external pathologies. At the end of the experiment there was no significant difference in these diets (P<0.01) in final weight, individual weight gain, individual food intake, food conversion ratio, and specific growth rate. Marked interlamellar lesions were observed in gills of fish fed on the lowest inclusion level diets. The lesions ranged from oedema, hyperplasia covering all the secondary lamellae to the complete fusion of adjacent filaments. These fish also developed necrosis of the pancreas, whilst fish fed diets up to 80 mg/kg showed marked glycogen deposition in the hepatic cells. For the first time it is reported that fish deficient in pantothenic acid showed ceroid deposition in the hepatic cells and spleen. Fish fed on diets containing 80‐320 mg/kg did not show external or histological changes. It is thus recommended that the diet ofC. urophthalmusfry must be supplemented with at least 80 mg/kg diet to give maximum growth and to avoid gross and histologicai signs of defici

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00451.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Gold and black Oreochromis mossambicus (Peters) fry were stocked in 0.043‐m3hapas along with early instar dragonfly nymphs to determine the effect of body colour of the tilapia on vuinerability to predation by the insect. Hapas were stocked with either: 10 gold fry, 10 black fry and no dragonfly nymphs (10‐10‐0); 5 gold fry, 5 black fry and 2 dragonfly nymphs (5‐5‐2); 10 gold fry, 10 black fry and 2 dragonfly nymphs (10‐10‐2); or 10 gold fry, 10 black fry and 3 dragonfly nymphs (10‐10‐3). Four levels of predation were assessed: no predation, 1 dragonfly nymph per 5 fish, 1 per 6.7 fish, and 1 per 10 fish. Hapas were censused daily for 14 days. Fish that had been eaten were replaced with similar‐sized fish to restore stocking densities. Average daily predation rate ranged from 0.24 to 3.0 and averaged 1.94 fry/dragonfly nymph/day. Average daily predation rates for all treatments were significantly (P = 0.05) different and were a function of both dragonfly and fish stocking rates. Dragonfly nymphs ate significantly more black fish than gold fish in the 10‐10‐2 and 10‐10‐3 treatments: overall (10‐10‐2, 10‐10‐3 and 5‐5‐2 treatments combined), dragonfly nymphs ate significantly more black (324) than gold (245) tilapia. Results from this study indicate that the bright body colour of the gold tilapia does not increas

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00452.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Gynogenetic (meiotic)Oreochromis mossambicus(Peters) lines can be produced easily with the simple ultraviolet (UV) spermatozoan irradiation technique detailed in this study. One hundred per cent haploid gynogens were achieved by eggs fertilized with UV‐irradiated (254 nm, 4.2 W/m2for 7 min) red tilapia spermatozoa. Survival of the haploid gynogens were 5% and all haploid fry were deformed. Hybridization between femaleO. mossambicusand male red tilapia produced 100% red offspring. Thus the red colour can be used as a marker to identify fish that are not gynogens. Activation of eggs with 7‐min UV‐irradiated spermatozoa from red tilapia and subsequent heat shocking at 420C for 3 min resulted in 100% diploid gynogens (b

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00453.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The reproductive biology of a popular and abundant freshwater catfish, Mystus nemurus Cuvier&Valenciennes, was examined, including sex ratio, gonadosomatic index, ova diameter and fecundity. The numerical ratio of male to female was 1:1.06 and was not significantly different (P>0.05). Mean female gonadosomatic indices (GSI) in April and September corresponding to north‐east and south‐west monsoons were significantly different (P0.05) in the fluctuation of the measure of GSI except for those in the dry months, which probably suggested the existence of a protracted breeding season. Mean male GSI in February and November were similarly significant (P0.05) from those of January, March, April, July, August, October and November. This was probably attributable to an extended breeding period with spawning peaks in February and November corresponding to early and late monsoons. The aseasonal reproduction is common in tropical fishes. GSI were positively correlated with rainfall and water level fluctuations. Fecundity varied from a minimum 6900 to a maximum 93510 in specimens with total lengths of 34.8cm and 45.0cm respectively. Fecundity was found to increase linearly with length and weight and was significantly different (P<0.05) from t

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00454.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Acute toxicity of Ca(OH)2, NPK, Na3PO412H2O and NaNO3fertilizers onClarias gariepinus(Teugals) was investigated in glass aquaria. Results showed that Ca(OH)3 was the most toxic of the four fertilizers. Na3PO4.12H2O and NaNO3 were less toxic. The 96‐h LC50 for the fertilizers ranged from 33.9 mg/l for Ca(OH)2 to 1258.9 mg/1 for NaNO3. It is concluded that secondary application of these fertilizers in stocked ponds should be avoide

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00455.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.In Kuwait, the culture of tilapia,Oreochromis spilurus(Günther), in sea cages is limited by water temperature for mid‐April to mid‐November only. Using fry spawned in April, one production cycle is passible, but marketing time is limited to less than 20 days. With a market capacity of 1 tonne/day, the production of 100 tonnes/year planned for a commercial farm requires 100 marketing days. It is therefore necessary to shorten production time by stocking larger fingerlings to extend the marketing period.Four fingerling production schedules were tested, using fry spawned (1) in May, grown normally; (2) in May, stunted; (3) in August; and (4) in December. The fish were initially stocked and overwintered in fibreglass tanks. On 19 April, the fish were transferred to 1‐m3net cages at 150 fish/cage and grown to marketable size (<300g).Results showed that fish spawned in May (normal and stunted), August and December were harvested in July, August and October and can be marketed for 125, 100 and 60 days, respectively. It is apparent that the production of 100 tonnes of tilapia to be marketed over a period of 100 days is possible using fry produced in August; the profit, however, is marginal. Fry spawned in December gave the highest

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00456.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Four 0.05‐ha research ponds were filled with brackish water (12 ppt) for the purpose of evaluating zooplankion dynamics and predator‐prey interactions. Three of the ponds were stocked with Chesapeake striped bass,Morone saxatilis(Walbaum). All ponds were fertilized to stimulate zooplankton blooms using a protocol that has been successful in freshwater systems. Zooplankton was dominated by four major groups: rotifers, copepod nauplii,Eurytemoraadults andEurytemoracopepedites with rotifers and the nauplii being the most abundant organisms found. Rotifer populations peaked 15‐20 days after filling while the copepods peaked 17‐22 days after filling. Fish production was very similar to that found in freshwater ponds with an average yield of 84.4 kg/ha (2.0 kg/ha/day) for phase 1 fish (=45mm). Food selectivity indices indicated striped bass avoided both rotifers and copepod nauplii and preferred adult and copepediteEurytemoraas a food item. However, due to various problems associated with sampling, these selectivity results should be considered with caution. The findings of this study reveal fertilization regimes used successfully in freshwater production systems can be applied in an estuarine envi

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00457.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The effects of three selected algal species,Tetraselmis tetrahele,Isochrysis galbanaand marineChlorellasp. on the population growth ofBrachionus plicatiliswas evaluated after 3, 5 and 7 days of culture. The rotifers fed onT. tetraheleshowed superior growth with mean peak density of 92.5 individuals per ml to those fed on I. galbana (48.2 individuals per ml) and Chlorella sp. (47.2 individuals per ml) in 5 days.In another experiment, milkfish.Chanos chanosForsskal, fry with initial mean body weight and standard length of 6.26 ± 1.07mg and 13.04 ± 1.40mm, respectively, were fedB. plicatilisreared on the three algal species for 30 days. Results showed that growth, measured in terms of gain in weight and length, was significantly different (P>0.05) among treatments. Fastest growth was obtained in fry fedB. plicatiliscultured onT. tetrahelewith mean gains in weight and length of 61.48 ± 8.40mg and 9.37 ± 1.68 mm, respectively, followed by fry fedB. plicatilisreared onI. galbana(43.56 ± 8.35mg and 6.25 ± 0.48mm). Milkfish fry fedB. plicatiliscultured onChlorellasp. gave the poorest growth with mean gains in weight and length of 11.05 ± 1.82mg and 2.33 ± 0.29mm, respectively. Percentage survival ranged from 93.1 to 95.3 percent and was not significantly different between treatments (P<0.05).The differences in population growth ofB. plicatilisand consequently growth of milkfish fry was almost certainly attributed to the differences observed in the biological values of their algal diet, and in particular their protein and lipid contents.T. tetraheleandI. galbanaimproved the food value ofB. plicatilisas live food for the milkfish fry. Their high dietary value was related to the higher algal protein and fat levels and contents of n‐3 HUFA particularly 20:5n‐3 and 22:6n‐3 compared toB. plicatiliscultured onChlorellasp. The results of the present study point toT. tetraheleas the most suitable food for the mass culture of the rotifer,

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00458.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.In the River Vardnes, in northern Norway, 4162 first time migrants and 996 older migrants of Arctic char,Salvelinus alpinus(L.), were tagged when descending and 682 were tagged when ascending. All migrating fish were tagged individually when they were caught for the first time. Tagging reduced the sea survival rate of the first‐time migrants by at least 28.8%. A high rate of tag loss is indicated. Tagging had no measurable negative effect on the survival of the larger‐sized char. No effect of tagging on either the seasonal or the daily growth‐rates was rec

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00459.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The efficiency of stocking with whitefish,Coregonus lavaretusL., fingerlings was assessed in a large lake system with a naturally reproducing local whitefish stock. After the start of the stocking programme, the whitetish catch increased. The proportion of stocked whitefish in the catch was ca. 50%. The calculated yield per thousand released fingerlings was 57 ± 18kg. Further, the efficiency of stocking may be indicated by the following facts. Prior to stocking, the whitefish catch decreased, evidently due to recruitment overfishing. It was suggested that this situation was corrected by stocking with fingerlings and the whitefish catch then increased. The catch per unit of effort (CPUE) generally decreases with increasing fishing effort, but in this case the CPUE remained at the same level in spite of a considerable increase in fishing effort. The growth rate depends on the density of the fish stock. In this case the growth rate declined, possibly due to the fact that fingerling stocking increased the population density

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1990.tb00460.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY