Effects of stocking densities on the growth, survival and production of mahseer (Tor putitora) fingerlings were examined in a single-stage nursery-rearing system. The experiment was conducted for 8 weeks in six earthen nursery ponds having an area of 0.012 h each. Four-day-old hatchlings stocked at 0.6 million/ha was designated as treatment-1 (T1), 0.8 million/ha as treatment-2 (T2) and 1.0 million/ha as treatment-3 (T3). At stocking, all hatchlings were of same age group with a mean length and weight of 1.18 ± 0.04 cm and 0.012 ± 0.003 g, respectively. Hatchlings in all the treatments were fed with Saudi Bangla (SABINCO) commercial fish feed viz., nursery (32.06% crude protein) for the first 14 days and starter-I (31.53% crude protein) from days 15 to 56. Physico-chemical parameters (temperature, secchi disc transparency, dissolved oxygen, pH and total alkalinity) and plankton populations (phyto- and zooplankton) were at the optimum level for fish culture. Highest weight gain was observed in T1 and lowest in T3. Final length, final weight and survival of fingerlings also followed the same trends as weight gain. Fingerlings in T1 produced significantly higher specific growth rate than T3, but not than T2. Feed conversion ratio was significantly higher in T1 followed by T2 and T3 in that order. Significantly higher number of fingerlings was produced in T3 than in T2 and T1, respectively. Despite this, consistently higher net benefits were obtained from T1 than from T3 and T2. Overall, highest growth, survival and benefits of fingerlings were obtained at a density of 0.6 million hatchling/ha. Hence, of the three stocking densities, 0.6 million hatchling/ha appears to be the most suitable stocking density for rearing of mahseer fingerlings in single-stage nursery system.

Olive barb (Systomus sarana) was collected from three different locations viz. Kuliarchar, Bhairab and Bikrampur in Bangladesh to elucidate genetic diversity by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). Six arbitrary oligonucleotide RAPD primers were used to amplify the DNA from each population. A total of 52 bands were produced in 3 olive barb populations where 28 bands were polymorphic indicating 53.84% polymorphisms in those three populations with an average of 9 bands per primer. The molecular size of the amplified DNA fragments ranged between 300 and 2300 bp. 12 unique RAPD bands were observed in the three populations. The bands are specific and stable and thus could be used to characterize each germplasm. The values of pair-wise genetic distances ranged between 0.5232 and 0.8109 with some degrees of genetic variation among the populations. The highest genetic distance (0.8109) was observed between olive barb collected from Kuliarchar and Bikrampur, while the lowest (0.5232) was found between olive barb collected from Kuliarchar and Bhairab. The UPGMA dendrogram segregated three samples of olive barb into two major clusters C1 and C2. The Kuliarchar-Bhairab population pair of olive barb was genetically closer than that of Kuliarchar-Bikrampur. Therefore, RAPD analysis can be used to identify the genetic diversity in olive barb. This information may be used for improved breeding programme and conservation of native olive barb.

The Padma River is one of the longest rivers and it is believed to be an important spawning and feeding ground for riverine fish species of Bangladesh. This study analyzed the fish biodiversity and main threats to biodiversity to provide recommendations for conservation in the Padma River. Sampling was conducted fortnightly in the Padma River during March 2009 to February 2010 from fishermen catch landed at different fish landing centers between Binodpur and Godagari, Rajshahi, northwestern Bangladesh. A total of 80 species of fish under 9 orders and 24 families were recorded. Cypriniformes were most dominant order constituting 35% of the total fish population followed by Siluriformes (32.50%), Perciformes (17.50%), Clupeiformes (5.00%), Synbranchiformes (3.75%), Osteoglossiformes (2.50%), Beloniformes (1.25%), Mugiliformes (1.25%) and Tetraodontiformes (1.25%). Among the species found during the present study, 12.50% were vulnerable, 21.25% were endangered and 8.75% were critically endangered. Major threats to fish biodiversity include habitat destruction and defragmentation, water pollution, indiscriminate harvesting of fry and fingerlings, construction of barrages, construction of embankments by the Ganges-Kobadak project, sedimentation. Restocking economically important fish species, establishing and maintaining fishery sanctuaries, ordering closed seasons and combining fisheries with aquaculture, banning indiscriminate fishing and destructive fishing gears, strengthening CBOs (Community based organizations), encouraging IPM (integrated pest management), dredging, identification and protection of the breeding and nursery grounds are recommended for the conservation of fish biodiversity in the Padma River, NW Bangladesh.

ABSTRACT: Two minnows, indigenous olive barb, Puntius sarana and exotic silver barb, Barbodes gonionotus are important fish species in Bangladesh. Therefore, it is essential to identify diversed population of these fish species for selective breeding programme. Sixty olive barb fish were collected from three different natural stocks (Mymensingh, Madaripur and Sylhet) and 20 silver barbs from hatchery stock of Jashore in Bangladesh. Out of 40 decamer primers tested, 5 primers were selected for the Polymerase Chain Reaction (PCR) based RAPD (Randomly Amplified Polymorphic DNA) analysis. Upon agarose gel electrophoresis, RAPD bands were scored as separately on the basis of their presence or absence for each sample and primer. A total of 43 polymorphic bands and highest proportion of polymorphic bands (62.79%) were found in the Madaripur populations. The gene diversity (0.2132±0.2067) and Shannon's Information index (0.3161±0.2950) within populations were highest in Jashore stock. Among olive barb stocks, these values were higher in Sylhet stock. Besides, four populations segregated in two main clusters based on the Nei's genetic distance. Indicating the segregation of two different species of minnows, the silver barb stock made one separate cluster while other three stocks of olive barb remained in another cluster. The present study exposed a distinct pattern of genetic variation and phylogenetic relatedness that would be helpful in selecting broodfish for genetic improvement as well as in conservation of these fish species.