Md. Akhtar Hossain

Sperm cryopreservation of the Indian major carp, Labeo calbasu: Effects of cryoprotectants, cooling rates and thawing rates on egg fertilization

A sperm cryopreservation protocol for the Indian major carp, Labeo calbasu, was developed for long-term preservation and artificial fertilization. Milt collected from mature male fish were placed in Alsevers solution (296mOsmolkg(-1)) to immobilize the sperm. Cryoprotectant toxicity was evaluated by motility assessment with dimethyl sulfoxide (DMSO) and methanol at 5, 10 and 15% concentrations. DMSO was more toxic at higher concentrations than methanol, and consequently 15% DMSO was excluded from further study. A one-step cooling protocol (from 5 to 80°C) with two cooling rates (5 and 10°C/min) was carried out in a computer-controlled freezer (FREEZE CONTROL(®) CL-3300; Australia). Based on post-thaw motility, the 10°C/min cooling rate with either 10% DMSO or 10% methanol yielded significantly higher (P=0.011) post-thaw motility than the other rate and cryoprotectant concentrations. Sperm thawed at 40°C for 15s and fresh sperm were used to fertilize freshly collected L. calbasu eggs and significant differences were observed (P=0.001) in percent fertilization between cryopreserved and fresh sperm as well as among different sperm-to-egg ratios (P=0.001). The highest fertilization and hatching rates were observed for thawed sperm at a sperm-to-egg ratio of 4.1×10(5):1. The cryopreservation protocol developed can facilitate hatchery operations and long-term conservation of genetic resources of L. calbasu.

THREATENED FISHES OF THE WORLD: Cirrhinus reba (Hamilton 1822) (Cypriniformes: Cyprinidae)

The threatened Reba carp Cirrhinus reba is one of the foods high in nutritional value in Asian countries, including Bangladesh, India, Nepal and Pakistan. However, natural populations have been declined due to overexploitation and various ecological changes in its natural habitats leading to an alarming condition and deserving high conservation importance. This paper recommends actions for the conservation of the remaining isolated population of C. reba in Asian countries.

THREATENED FISHES OF THE WORLD: Eutropiichthys vacha (Hamilton, 1822) (Siluriformes: Schilbeidae)

River catfish Eutropiichthys vacha is one of the foods high in nutritional value in Asian countries. However, natural populations have seriously declined or are on the verge of extinction due to over-exploitation and various ecological changes in its natural habitats, leading to an alarm- ing situation which deserves high conservation attention. This paper suggests conservation measures that should be taken into account to- wards the preservation of the remnant isolated population of E. vacha in Asian countries.

Effects of Stocking Density on Production and Economics of All-Male Tilapia (Oreochromis niloticus) Culture in a Rain Fed Rice-Fish Ecosystem

Abstract Effects of stocking density on the growth, production, and economics of all-male tilapia (Oreochromis niloticus) were investigated in a rain-fed rice-fish ecosystem for a period of 120 days. Fish were stocked at the rate of 4000, 5000, and 6000 ha−1 in treatments T1, T2, and T3, respectively. Water quality was suitable for fish culture. Significantly higher growth was observed in T1 as compared to other treatments. SGR ranged from 1.26 to 1.51. Survival varied between 79% and 88% with treatment T1 producing the highest survival. The highest benefit:cost ratio was obtained in T2 followed by T1 and T3. The best fish production (457.21 kg ha−1) and economic return for the culture period was obtained at 5000 fish ha−1.

Effects of supplementary feeds with different protein levels on growth and economic performances of Nile tilapia (Oreochromis niloticus) cultured in a rain-fed rice–fish ecosystem

ABSTRACT This study investigated the effects of supplementary feeds with different crude protein (CP) levels on the growth and economic performances of sex-reversed Nile tilapia (Oreochromis niloticus) reared in a rain-fed rice–fish ecosystem for a period of 120 days. There were four treatments—namely, traditional feed (21% CP), formulated feed (26% CP), commercial feed (30% CP), and control (no feed was used)—with three replicates per treatment. Fish (30.04 g) were stocked in ditches at a rate of 0.5 fish m−2 considering the total area and fed one of the tested feeds twice daily at the rate of 2%–5% of body weight. Water-quality parameters of the ditches were monitored fortnightly, and these parameters were found suitable for fish farming. Organic matter, total nitrogen, and available phosphorous in soil were increased significantly (P < 0.05) in the feed treatments after fish cultivation. Highly significant weight gain and SGR were observed with fish fed the commercial feed as compared with other treatments. The highest benefit-cost ratio (2.15) was found in the control, followed by formulated feed (1.90), but in the case of numerical net return, it was the opposite. However, commercial feed showed the lowest benefit-cost ratio (1.67) due to higher feed cost than other supplementary feeds. Therefore, this study suggests that fish fed with a formulated feed (26% CP) produced significantly higher net economic return in the rice–fish farming system.