The present study was aimed at the identification of treatment optima to induce triploidy in ‘Labeo rohita (rohu) × Cirrhinus cirrhosus (mrigal)’ hybrid using heat shock treatment. The eggs were exposed at four different temperature regimes viz., 38, 39, 40 and 41°C for 1–3 min, applied 3–5 min after fertilization. After 4 min of fertilization, heat shock treatments for 1 and 1.5 min durations were found the best inducing triploidy up to 100% and 96% respectively. Survival rates upto yolk sac absorption were found to be 73% and 71% in rohu and mrigal, 68% and 67% in the reciprocal diploid hybrids and 61% and 60% in the reciprocal triploid hybrids (RTH). Triploidy was confirmed by chromosome counting that revealed the diploid chromosome number of rohu and mrigal at 2n = 50 and in their triploid hybrid chromosome number was found to be 3n = 75. Growth rate of the RTH showed a significant difference (P < 0.05) from the single species and the diploid hybrids. Triploids also showed higher survival rate over the diploids.

As a genetic means of aquaculture development, hybridization can increase production quickly in fishes because of heterotic effect. At the backdrop of reports on the decline of growth and reproduction of the hatchery population of Labeo rohita in Bangladesh, a 3 months study was undertaken to see the heterotic effect by intra-specific crossing among the Padma, Jamuna and Hatchery strains of rohu. Six reciprocal crosses and 3 pure crosses were obtained. The fertilization and hatching rates of the developing embryos were found better in the parental crosses than the reciprocal intra-specific hybrids. The growth performance of reciprocal crosses showed significant differences (P< 0.05) over the parental crosses. The best growth performance was observed in Padma ? X Jamuna ? hybrids; providing 72% positive heterosis. Since the growth rate of strain crossed hybrids were reasonably high, this technique can be profitably applied for the production of fast growing seed to ensure higher fish production and more profit.DOI: http://dx.doi.org/10.3126/ijls.v5i1.5035 International Journal of Life Sciences Vol.5(1) 2011 32-38

Probiotic Shrimp Lactobacillus Antagonistic effect AquacultureThe present study was conducted to study in-vitro the antagonistic effect of Lactobacillus spp. against the pathogenic bacterial vibrio harveyi on shrimp. For this purpose, shrimp samples were collected from three different Ghers at Batiaghata upazilla, Khulna. Gills and intestines were taken out from the samples to identify the load of Lactobacillus spp. and Vibrio spp. The results revealed that the load of Lactobacillus spp. was found more than Vibrio spp. both in gills and intestines; the gills also contained higher load of Vibrio spp. than in the intestines. V. harveyi was separated from the isolated Vibrio spp. with different types of biochemical tests: Gram stain, Motility test, Indole test, VP test, MR test, Arginine dihydrolase, Salt tolerance test, growth at different temperature ranges and colony color on TCBS agar media. The isolated V. harveyi was subjected for in-vitro test. In in-vitro challenge test, the potential antagonistic effect of Lactobacillus spp. against V. harveyi was gradually obtained at 0, 4 th , 8 th , 12 th hour of treatments. Interesting finding was that, with the time, the load of V. harveyi was reduced gradually and the lowest load was obtained after 12 hours of probiotic inoculation. The present study revealed an excellent in-vitro antagonistic probiotic effect of Lactobacillus spp. on V. harveyi. Therefore the result suggested that probiotic treatment might be an effective alternative to the use of antibiotics in treatments of bacterial diseases in shrimp aquaculture.