Ashfaqun Nahar

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.

OVER-WINTERING GROWTH PERFORMANCE OF MIXED-SEX AND MONO-SEX NILE TILAPIA Oreochromis niloticus IN THE NORTHEASTERN BANGLADESH

The study was conducted to assess the over-wintering growth performance of mixed-sex and mono-sex male tilapia, Oreochromis niloticus. The experiment was carried out with two treatments each with three replicates for a period of 6 months from October 2012 to March 2013 in the Field Laboratory Complex, Bangladesh Agricultural University. In the first treatment (T 1 ), mixed-sex tilapia was stocked in 3 ponds with a mean initial weight of 4.80±0.18 g. In the second treatment (T 2 ), mono-sex male tilapia was stocked in another 3 ponds with a mean initial weight of 4.81±0.20 g. Fish were fed at the rate of 6% of fish body weight at the beginning of the experiments, then the feeding rates were gradually reduced to 2% for the third month and finally increased to 3% for the rest of the period. Water parameters in terms of temperature, dissolved oxygen, pH, transparency, alkalinity, ammonia and nitrite were within the range of fish farming. After 6 months of culture period, mono-sex male tilapia attained a significantly (P 0.05) difference of food conversion ratio and survival rate (%) values between the treatments. The benefit-cost ratio was calculated as 1.17 and 1.43 for mixed-sex and mono-sex male tilapia, respectively. The results suggested that it is possible to successfully culture tilapia during the winter period in Bangladesh, and the culture of mono-sex tilapia is more profitable due to its higher growth rate.

Variation in the life-history traits of a Schilbid catfish, Clupisoma garua (Hamilton, 1822) in the coastal waters of southern Bangladesh

For the first time, the present study reports the life-history traits, comprising length-frequency distribution (LFD), sex ratio (SR), length-weight relationships (LWRs), condition factors (CFs), and relative growth (WR), of Clupisoma garua in the coastal waters of Bangladesh. A total of 150 specimens ranging from 8.60 to 25.20 cm total length (TL) and 4.26 to 128.80 g body weight (BW) were collected using traditional fishing gear from August 2013 to July 2014. The overall sex ratio of males to females in the study did not differ significantly from the expected value of 1:1 (χ2 =0.96, P <0.05) but there were significant sex differences (P <0.05) in the intercepts and slopes of graphs characterizing traits in C. garua. The calculated b values for the LWRs were 2.955, 2.893 and 2.927 for males, females and combined sexes, respectively, and there was negative allometric growth in all cases (b <3). The condition factors (KA, KF, KR) and relative growth (WR) also did not differ significantly ( P <0.05) between the sexes. This study provides a useful tool for fishery specialists to evaluate the relative condition of fish and to initiate early management strategies and regulations for the sustainable management of the remaining stocks of this species in the entire coastal region of southern Bangladesh.

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

First record of the razorbelly scad Alepes kleinii (Bloch, 1793) (Carangidae) along the coast of Bangladesh

BackgroundThe Bay of Bengal coast, Bangladesh is a hotspot of fisheries abundance and diversity. A new species of Carangid family Alepes kleinii is recorded and described for the first time in the coastal waters of Bangladesh.ResultsA total of 29 individuals of Alepes kleinii were collected from the surveyed areas between January to March, 2016. Validation of this species was confirmed by phenotypic characteristics including body and fins colour, shape, vertical stripes, number of fin rays etc. which were found to be identical to that of the Alepes kleinii described in existing literature. The regression parameter value (b = 2.81) of the length-weight relationship (W = aLb) indicates that the Bay of Bengal provides favourable environmental conditions for the growth and development of this species.ConclusionThe discovery of the razorbelly scad in these waters provide valuable information regarding species distribution and extension, location and habitat preference. This information is prerequisite for the sound management of the coastal fisheries of Bangladesh.

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.

Fish Community Structure of Sandha River: A Link Analysis towards FisheriesManagement and Conservation

Sandha River water regime is used as a nursery, feeding and breeding places by commercially important fish species due to the presence of unique environment. Therefore, the present study has been conducted to assess water quality parameters, fish species abundance, fish diversity indices, conservation issues and management policy to guard the valuable aquatic resources of Sandha River from March 2015 to February 2016. Among the water quality parameters, temperature and pH were found at a slight rising level which possessed insignificant negative correlation with fish species abundance (p<0.01). Fish diversity indices were calculated of which the value of Shannon-Wiener Index just above 3 which indicated the river ecosystem still approving good fish community structure where lower value of richness described short food webs. Garretts Ranking Technique was applied to identify the reasons behind the decline of Sandha River fish species over the periods. The study, therefore, concluded that the river has experienced with slight climate modifications and significant anthropogenic activities especially huge fishing pressure which in a feedback reduce the fisheries stock resources with time. Community-based fisheries management (CBFM) hence would be an appropriate tool to make the water resources sustainable.

Stock Structure of the Critically Endangered Clupisoma garua (Hamilton,1822): An Investigation Based on Discriminant Analysis Approach

The stock structure of critically endangered Clupisoma garua were examined based on morphometric characters. A total of 133 specimens were collected from four rivers located in the southern coastal zone of Bangladesh. Data were subjected to principal component analysis, discriminant function analysis and univariate analysis of variance. In discriminant function analysis, plotting first and second discriminant functions explained 88.4% and 9.9% of the between-group variation for morphometric analyses indicating the existence of three morphologically differentiated groups of C. garua. The first principal component (PC1) explained 82.41% of the total variation, while PC2 explained 4.62%. The step-wise discriminant function analysis (DFA) retained six variables that significantly discriminated the populations. Using these variables, 82.0% of the original groups were classified into their correct samples and 79.70% of the cross validated groups omitting one procedure were classified into their correct samples. The result obtained from the study noticed significant differences among the populations.