LARVAL FISH IDENTIFICATION USING MORPHOLOGY AND TEMPORAL DISTRIBUTION AT THE BAKKHALI RIVER ESTUARY, COX’S BAZAR, BANGLADESH

Abstract

The temporal abundance and composition of fish larval families and their spawning season in the Bakkhali river estuary of Cox’s Bazar coast were studied from March 2020 to February 2021. Sampling was performed by a bongo net with two mouth openings. In total 883 individuals, representing 11 larval families, with a mean abundance of 73.58 individuals per 1000m3, were collected and identified under stereo microscope in this sampling period. Larvae that were found in this area were: Clupeidae, Ambassidae, Engraulidae, Gobiidae, Sillaginidae, Mugilidae, Megalopidae, Blenniidae, Terapontidae, Sparidae, and Gerreidae. Among them, Clupeidae, Ambassidae, and Engraulidae contributed 56.41%, 34.05%, and 2.95% of the total catch. The month of June was shown as the most diversified month, which had 94 individuals/1000m3. In contrast, May had the highest number of larvae families (06). Based on the constancy of occurrence, Clupeidae and Ambassidae were termed as "constant" as their larvae were found in seven months of that year. They spawn in summer, winter and monsoon. Most of the families (07) spawn in summer (March to June) and use this estuary as their nursing ground. The highest value of the Shannon-Wiener index was 1.055, observed in September. Both Margalef’s and Pieulo’s index were the highest in November, with 0.91 and 0.918, respectively. However, the diversity of larval assemblages in this estuary seems lower than in most other tropical estuaries. This study will establish the groundwork for sustainable fisheries resource management strategies in the Cox's Bazar region.