Sultan Mahmud

FISH DIVERSITY IN THE SOUTHERN COASTAL WATERS OF BANGLADESH: PRESENT STATUS, THREATS AND CONSERVATION PERSPECTIVES

Despite the enormous anthropogenic and environmental hazards affecting wild fisheries resources, southern coastal waters are still considered one of the aquatic biodiversity hotspots in Bangladesh. Therefore, the present study was conducted to make a complete account of fishes and to assess their condition and conservation status in the rivers spread across four southern coastal districts of Bangladesh. During the study period from January to December 2014, a total of 98 species of fish were recorded belonging to 81 genera, 48 families and 13 orders. Perciforms were recorded as the most diverse fish group in terms of both number and individuals of species observed. Of the 98 species, 26.53% were listed as Locally Threatened in Bangladesh, including 11.22% species listed as Vulnerable, 10.20% as Endangered and 5.10% as Critically Endangered. Four population indices viz, Shannon–Wiener index (H), Simpson’s dominance index (D), Simpson’s index of diversity (1-D) and Margalef’s index (d) were applied to demonstrate the species diversity, richness and evenness of fish in sampling areas and their overall values were 3.54-3.70, 0.04-0.05, 0.95-0.96 and 7.48-8.67, respectively. To sustain the prospect of fisheries biodiversity in the southern coastal areas of Bangladesh, management and conservation strategies like restocking economically important fish species, establishing and maintaining fish sanctuaries, banning indiscriminate fishing and destructive fishing gears, identification and protection of the breeding and nursery grounds should be taken into consideration with utmost priority.

Morphometric Parameters and Allometric Growth in Paradise Threadfin Polynemus paradiseus (Linnaeus, 1758) from a Coastal River of Bangladesh

Morphological parameters comprising length-weight relationships (LWRs), sex ratio, condition factor (KF) and allometric growth of paradise threadfin, Polynemus paradiseus from the southern coast of Bangladesh were estimated. A total of 221 specimens were collected with the help of local fishermen ranging size 8.30-13.70 cm standard length (SL) and 11.64-50.67 g body weight (BW) during the period of January to October, 2104. The overall sex ratio of the samples did not reveal significant variation from the expected value of 1:1 (male: female=1:0.99, χ2=0.004, P < 0.05). Length-frequency distribution revealed a size predominance of males over females, where mean variation of males consistently exceeded that of females throughout the year. The allometric coefficient b of LWR significantly deviated from 3 indicating allometric growth in males and females. The analysis of covariance (ANCOVA) showed significant differences in slope and intercept between the sexes (P < 0.001). KF by month in both sexes indicating the fishes were thriving very well in the coast of Bangladesh. This study reports the first findings regarding the LWRs, sex ratio and KF of Polynemus paradiseus in the coastal waters of Bangladesh

Potential Contribution of Fish Feed and Phytoplankton to the Content of Volatile Terpenes in Cultured Pangasius (Pangasianodon hypophthalmus) and Tilapia (Oreochromis niloticus)

Geosmin and 2-methylisoborneol are the most recognized off-flavors in freshwater fish, but terpenes may also contribute off-flavor in fish. We identified six monoterpenes, 11 sesquiterpenes, and three terpene-related compounds in pangasius and tilapia from aquaculture farms in Bangladesh. The concentrations of most of the volatiles were below published odor thresholds, except for α-pinene, limonene, β-caryophyllene, α-humulene, and β-ionone in tilapia, and limonene and β-ionone in pangasius. To identify sources of the terpenes, terpene profiles of fish feed and phytoplankton in the ponds were analyzed. In feed and mustard cake (feed ingredient), five monoterpenes and two sesquiterpenes were identified, and five of these compounds were also detected in the fish. In phytoplankton, 11 monoterpenes were found and three also occurred in the fish. The higher number of terpenes common to both fish and feed, than to fish and phytoplankton, suggests that feed was a more abundant source of odor-active terpenes in the fish than phytoplankton.

The Current Status of Small Indigenous Fish Species (SIS) of River Gorai, aDistributary of the River Ganges, Bangladesh

Small indigenous fish species (SIS) play a vital role in providing animal protein sources for human. The Gorai river, a Ganges tributary is a habitat of considerable number of SIS. A total of 11040 individual from 40 species were collected belonging 7 orders and 19 families using 5 fishing nets and 1 fish trap of which 2 species were critically endangered, 7 endangered, 7 species vulnerable, 18 species not threatened, 2 data deficient and 4 species were not in evaluated category. Dominant orders were Cypriniformes and Perciformes each contained 12 species, dominant family was Cyprinidae (11 species) and most dominant species was Chela cachius (2253 individuals). Diversity indices ranges from Simpson’s dominance index (0.06-0.09), Simpson’s index (0.91-0.94), Shannon Weiner index (3.08-3.24), Evenness (0.56-0.66), Menhinick’s index (0.61-0.67), Margalef’s index (4.48-4.77), Equitability (0.84-0.89) and Fisher alpha (5.86-6.31), respectively. Highest numbers (38) of SIS were caught by set bag net. Maximum total length 4.6 cm of Corica soborna was the new record. Considering the nutritional importance and reducing number of SIS inhabiting in the river Gorai, the present study aimed at documentation of SIS, their threatened status and conservation of SIS through laws and regulations.

Effect of probiotic and sand filtration treatments on water quality and growth of tilapia (Oreochromis niloticus) and pangas (Pangasianodon hypophthalmus) in earthen ponds of southern Bangladesh

ABSTRACT Effects of water treatment by two probiotic products (PondPlus® and AquaPhoto®) and sand filtration were studied on growth performance of tilapia (Oreochromis niloticus) and pangas (Pangasianodon hypophthalmus) stocked at tilapia:pangas ratio of 5:3 in traditional earthen ponds in Bangladesh. The fish were stocked at a density of 20,000 fish ha−1 and reared for 7 months. Compared to untreated ponds, treatments of probiotic products or sand filtration in earthen ponds resulted in a higher O2 content, higher water transparency, less ammonium, and fewer cyanobacteria. Weight gain for individual tilapia was lowest in the AquaPhoto-treated ponds (177 g), while similar gains (188–194 g) occurred in the other ponds. For pangas, the lowest weight gain (627 g) was obtained in the sand filter-treated ponds, as compared to 690–797 g in the other ponds. Thus, a general positive effect from the treatments on fish growth was not observed, possibly due to a reduced content of detritus (supplementary feed for both fish species) in the treated ponds.