Rearing of catfish (Clarias batrachus Lin.) larvae with live and prepared feeds

Provision or live feed (Tubificid worms) attributed significantly better weight gain in the five days old Clarias batrachus larvae when reared for another 28 days compared to those fed mixed feed (live and artificial) and artificial feed only. Larvae fed mixed feed showed significantly better weight gain compared to those fed only artificial feed and the survival rate was similar to those fed only live feed. Both the weight gain and survival rate were the lowest for the larvae reared only on artificial feed.

Growth and survival of Clarias batrachus (Lin.) larvae fed on formulated diets

An experiment was conducted for a period of 28 days using 7-day old C. batrachus larvae of initial total length (±S.D.) of 7.4 ± 0.49 mm and weight (±S.D.) of 2.8 ± 0.75 mg. Five test diets viz. diets I, II, III, IV and V were prepared. Diet I was formulated using 30% fish meal (FM), 20% soybean meal (SM) and 20% Baker's yeast (BY), diet III using 15% FM, 20% SM, 15% cotton seed meal and 30% BY and diet IV using 20% FM, 30% BY and 30% powdered milk. The remaining two diets (diets II and V) were prepared using minced clam meat (96%) and BY (90%) respectively as the sole source of protein. Three replications were used for each treatment. The larvae fed on diet II exhibited significantly (P<0.05) better length gain and specific growth rate (SGR) than those of the larvae fed on diet III and there was no significant difference among the length gain and SGR of the larvae fed on diet I,II,IV and V. The larvae fed on diet II also showed significantly better weight gain and survival than those of the larvae fed on other diets. There was no significant difference between the condition factor of the larvae fed on diet II and IV. However, the larvae fed on diet II showed better condition factor than those of the larvae fed on other diets.

Colossal loss of shell and fin-fish larvae during collection of Penaeus monodon (Fab.) fry in the rivers of Satkhira

This study was conducted in five river-estuaries of Satkhira from January to December '96. It was found that during the collection of each Peneaus monodon) post larva (PL), about 45 larvae of other shrimps, 12 individuals of fin-fishes and 530 macro-zooplankters were mercilessly destroyed. It was also recorded that about 11.6 million of P. monodon PLs were harvested annually from the study area. The sh1dy implies that colossal loss of shell and fin-fishes and other plankton resources is done by tiger shrimp fry collectors, and such massive destruction adversely affect the natural productivity and ecological balance of the coastal environment.

Minimization of cannibalism of African catfish (Clarias gariepinus Burchell) larvae in indoor culture system

For minimizing cannibalism of African catfish (Clarias gariepinus) larvae two trials for a period of 14 and 15 days respectively in four aquaria of size 120x49x32 cm³ were conducted. Seven days old African catfish larvae with an initial total length and weight of 7.84 (±0.40) mm and 4.40 (±1.18) mg respectively in the first trial and similarly 7.52(±0.61) mm and 3.98 (±0.56) mg in the second trial at the rate of same stocking densities of 2500 larvae in each aquarium were stocked in both trials. Cannibalistic larvae were separated by using grader frame from each treatment at 7 days and 5 days interval during first and second trial respectively. Two mesh sizes i.e., 5 mm and 7 mm were used in the grader frame in both trials. Survival rate was significantly higher in T1 than that of T2 in each trial. Grading of larvae with 5 days interval resulted higher survival rate than that of 7 days interval.

Dietary cholesterol requirement of larvae and postlarvae of the prawn Penaeus indicus (H. Milne Edwards)

Two sets of experiments were conducted to determine the dietary cholesterol requirement of larvae and postlarvae 1-10 of Penaeus indicus. Seven approximately isocaloric and isonitrogenous purified experimental diets were tried with graded levels of cholesterol ranging from 0 to 4%. The control feed for larvae and postlarvae 1-10 were phytoplankton and compounded feed NPCL-17, developed by CMFRI, Cochin respectively. Result of these experiments indicates that cholesterol is an essential nutrient in the diet of larvae and postlarvae 1-10. Survival and growth of larvae and postlarvae 1-10 were greatly affected by cholesterol deficiency in the diet. The optimal cholesterol requirement for larvae appeared to be 0.5% of the diet, while it was higher for postlarvae where inclusion of cholesterol at a level of 2% in the diet gave higher growth.

Economic feasibility of composite fish culture in leased-in village tanks of Kanyakumari district: an invesment analysis

Kanyakumari district belonging to the high rainfall zone has resource advantages for composite fish culture in the leased-in village tanks. There are more than 400 fish farmers operating in leased-in tanks following composite fish culture under the FFDA programme. To estimate the economic feasibility and financial viability of the enterprise, the present study was taken up. 38 fish farmers selected from the district provided the necessary information like capital investment, costs and return and constraints. The data collected were analysed and a farm nearest to the average farm situation was taken as the representative farm. Investment criteria like PayBack Period (PBP), Simple Rate of Returns (SRR), Net Present Value (NPV) and Benefit Cost Ratio (BCR) were estimated taking into account a period of 10 years, the period for which the village tanks are leased-out to fish farmers under the FFDA programme. The analysis indicated the profitability of composite fish culture in village tanks in the district and the results are discussed with recommendations.

Substitution of Artemia with Brachionus in different ratios during larval rearing of Macrobrachium rosenbergii and evaluation of their feed efficacy

Larval growth during stage I-VIII was studied in Macrobrachium rosenbergii. Duration in moult periodicity were recorded-during larval development period, larvae were fed with Brachionus (grown on Baker's yeast and also Brachinous raised through organic manuring in outdoor culture containers). The performance of the feed was evaluated through substitution of Brachionus in the feeding protocol, in lieu of Artemia 1st instar. The Artemia, Brachionus substitution ratio of 75:25 was found to be most efficient. The study also indicates that the comparative growth rate of Brachionus plicatilis is higher in manure loaded tanks than with Baker's yeast. Growth rate "Y'' in culture tank being 0.245 and 0.112 and corresponding duplicating time (Td) too was found to be 2.855 and 6.365 respectively in tanks manured/enriched with pig manure.

Bothid larvae (Pleuronectiformes-pisces) of the Gulf od Thailand and South China Sea

The larvae of bothids were found to be sparsely distributed in the Gulf of Thailand and South China Sea being only 11.9% in the Naga Expedition Collections. They were confined mostly to the coastal waters and were found in near shore stations situated between Bangkok and Saigon. Their density was high in the Gulf of Thailand. The larvae seem to prefer darkness with greater incidence during April 16 to October 15 period, with a peak in the collections taken during April. This report includes the occurrence of 17 species belonging to 6 genera collected from the Gulf of Thailand and South China Sea, along with their regional, seasonal as well as diurnal variations

Evaluation of some formulated diets for rearing the post-larvae of Macrobrachium rosenbergii

Macrobrachium rosenbergii post-larvae with an average weight of 6.26 ± 0.23 mg and an average length of 10.67 ± 0.13 mm were fed with one of the five experimental diets having graded levels of lipid (5.0, 7.5, 10.0, 12.5 and 15.0%) to satiation two times a day to study their effect on growth, survival and feed utilisation. The highest weight gain was observed in post-larvae fed 7.5% lipid, although there was no significant difference (p>0.05) between groups fed 7.5 and 10.0% lipid. Similar effect was observed in the specific growth rate and protein efficiency ratio of post-larvae fed the diet with 7.5 and 10.0% lipid. The lowest feed conversion ratio was obtained in postlarvae fed the diet with 7.5% lipid. The survival rates of post-larvae fed on various levels of dietary lipid differed significantly (p<0.05) after 15 days of rearing period. Significantly lower survival was observed in the diet with 15.0% lipid level. Dietary lipid did not significantly affect prawn carcass protein, lipid and ash contents. Based on the data analysis (ANOVA – one way analysis), the dietary lipid requirement for 15 days of nursery rearing of Macrobrachium rosenbergii post-larvae was estimated to be 7.5 to 10.0% under experimental conditions in this study.

A preliminary study of two village tanks (reservoirs) in the Polonnaruwa area with biological notes on these reservoirs in Ceylon

The present study was initiated in conjunction with a project to utilize some of these small tanks as fishponds by introducing desirable species like Tilapia mossambica Peters and harvesting them at the end of a single season which may vary from 4-8 months depending on the reservoir. Two reservoirs Timbirigaswewa and Dalukanawewa were chosen for this study. Both of these are in the Polonnaruwa area (Fig. 1). Timbirigaswewa (Fig 4) is as all rain fed tank of about 30 acres while Dalukanawewa (Fig. 2) is stream fed with an acreage of just over 100.

Results of the Austrian-Ceylonese hydrobiological mission 1970 of the 1st Zoological Institute of the University of Vienna (Austria) and the Department of Zoology of the Vidyalankara Campus of the University of Ceylon. Pt. 11. Larvae and pupae of water beetles collected from the islands of Ceylon

Water beetle larvae and pupae were collected from the lotic biotopes in localities of the southern part of Ceylon. The species are described and findings are related to previous investigations. The following families were represented: Dytiscidae, Gyrinidae, Hydrophilidae, Helodidae, Dascillidae (Eubrianacinae), Dryopidae and Lampyridae.

Results of the Austrian-Ceylonese hydrobiological mission 1970 of the 1st Zoological Institute of the University of Vienna (Austria) and the Department of Zoology of the University of Ceylon Vidyalankara Campus, Kelaniya. Pt. 12. Contributions to the ecology of the larvae of some Odonata from Ceylon

The Austrian-Ceylonese hydrobiological mission studied 38 biotopes; 28 of which contain Odonata. From the Zygoptera the Calopterydoidea seem to be the dominant form (22 habitats), while the Coenagrionoidea are scarcer (11 habitats). The most frequent species was Euphaea splendens (Epallagidae - 16 habitats) followed by Vestolis apicalis nigrescens (Calopterygidae, 8 habitats) and Neurobasis chinensis (Calopterygidae, 6 habitats). From the Anisoptera Zygonyx ceylanica (Libellulidae: Zygonictinae) was the dominant form (8 habitats), but some Libellulinae remain undescribed. The number of species varied greatly between different biotopes. The biotopes containing Odonata are small brooks, in which the pH was mostly on the limit between acid and alkaline reaction. They are fast running waters, situated in most cases on lower or middle elevations, only three species being found in higher elevations (1800-2000 m). Adaptations to fast currents and other factors are described.

Effect of combined thyroxine and cortisol treatment on hatching of eggs, post-embryonic growth and survival of larvae of Heteropneustes fossilis

In order to record the effects of thyroxine and cortisol (individual/combined) on hatching, post-embryonic growth and survival of larvae of Heteropneustes fossilis, newly fertilized eggs were given bath immersion treatments of L-thyroxine (T sub(4); 0.05 mg/l), cortisol (0.50 mg/l) and T sub(4)+ cortisol (0.05 mg/l+0.50 mg/l) for 15 days. Hatching of eggs, growth and survival of the larvae improved significantly (P<0.001) in the hormone treated groups as compared to those of control. The frequency of deformities was reduced in the combined hormone treatment group. The present observations suggest that the advanced digestive function probably induced by T sub(4)+cortisol treatment might have resulted in improvement in food utilization during the critical phases of first feeding and promoted vital developmental processes resulting in uniform growth, decreased mortality, better survival and transformation of larvae to juveniles. This combined hormone therapy appears to have practical utility in fish hatchery practice for better success in larval rearing.

Use of crude salt in rearing of freshwater giant prawn, Macrobrachium rosenbergii (de Man) larvae

Three different types of culture media: (i) 100% brine (B 100 ), (ii) 75% brine and 25% crude salt (B 75 CS 25 ), and 50% brine and 50% crude salt (B 50 CS 50) were tested to evaluate the possible use of brackish water reconstituted from the crude salt for the production of M. rosenbergii post-larvae. The production rate of 25.26±0.20 PI/l with a corresponding survival rate of 84.20±0.66% was significantly higher (P<0.05) for the larvae reared on B100 than that of 22.10±0.57 Pl/l with a corresponding survival rate of 73.68±1.89% on B50CS50. Larvae cultured on B75CS25 did not show any significant difference (P<0.05) in production as well as in survival of post-larvae than that on B100. The result shows that, for rearing of prawn larvae, use of brine can be replaced up to 25% without any undue reduction in production of post-larvae. However, the production as well as survival rate of post-larvae with 50% replacement (B50CS50) is also appreciable. It is assumed that the mineral constituents of natural seawater might have some triggering effects on prawn larvae in closing their larval cycle.

Description of stomatopod larvae from the Arabian Sea

The Northern Arabian Sea Ecological and Environmental Research (NASEER) Programme cruise I, January, 1992 and other collections from Manora Channel (Karachi) were examined. Six stages i.e. IV, VII, VIII, IX, X and XI of stomatopod larvae are recognized. Day samples talen in 1994 (January to December) from Manora Channel revealed the presence of only three specimens of stage IV. They all belong to the family Squillidae. Each stage is measured, described and illustrated. None of the stages could be correlated to their adults.