The western rainbowfish (Melanotaenia australis) is one of the most common and highly abundant freshwater fish endemic to north-western Australia. It shows extensive geographic variation in their colour pattern. Genetic study revealed spatial population structure in this species that could be a possible threat to its existence. Therefore we designed and isolated 15 highly polymorphic microsatellite markers for M. australis for use in population studies across its distribution. We screened these primers across 32 individuals from the Daly River and found between 4 and 22 alleles per locus. The observed heterozygosities ranged from 0.345 to 1.000. These markers will be now available for future studies of population structure across its natural range and to assist in management as well as future conservation.

Summary The present study describes the length–weight (LWR) of three fish species, Chela cachius (Hamilton, 1822), Coilia ramcarati (Hamilton, 1822) and Sardinella gibbosa (Bleeker, 1849) captured in the Bay of Bengal, Bangladesh, from December 2014 to November 2015. Fishes were captured with either gill nets (mesh size 2.0–5.0 cm) or set bag nets (mesh size 2.0–4.0 cm). The b values in the study varied from 2.88 (C. ramcarati) to 3.00 (S. gibbosa), with a mean a value of 2.94 at p < .001 for all three species. In addition, the study provides initial information on LWRs for C. cachius and C. ramcarati and maximum length records for C. cachius and S. gibbosa.

The present study was undertaken to estimate genetic diversity and reveal population structure of Hilsa shad (Tenualosa ilisha) from two large river ecosystems, the Padma and Meghna of Bangladesh using mitochondrial control region (D-loop region). Fin tissue samples of 60 individuals were collected from the Padma (ChapaiNawabgonj) and Meghna River (Chandpur). DNA was extracted and D-loopof mtDNA was amplified, purified and sequenced. A total of 35 Sequences (15 Sequences from the Padma and 20 Sequences from the Meghna population) were analyzed and 14 haplotypes were detected. Total16 polymorphic sites were identified that included11 singleton sites and 5 parsimony informative sites. These populations showed high haplotype diversity (h) (0.863 in the Meghna and 0.901in the Padma population). We found low nucleotide diversity (Pi) within each population, 0.0058±0.0039 in the Padma to 0.0063±0.004 in the Meghna population. The shared haplotypes among the two populations were identified as 28.57%, and the rest 71.43% were private haplotypes. Estimate of genetic differentiations (Fst) suggest that the Meghna population of Hilsa was closely related to the Padma population (Fst= 0.058, P=0.07). The TCS genealogy showed three main haplotypes separated by three mutational steps and hap_10 might be the most ancestral haplotype by its internal position in the network. All results suggest panmixia in T. ilisha populations between the Meghna and Padma river populations and thus similar management plan could be useful for these two river Hilsa fishery in Bangladesh.

Black pomfret (Parastromateus niger) is one of the major commercial species of pomfret fishery in Bangladesh. This study illustrates the population structure (Length Frequency Distribution, LFD), relationship between length and weight (LWR), relationships between length and length (LLRs), Fulton’s condition factor (KF) and relative weight (WR) of P. niger in the Bay of Bengal (BoB). A total of 225 P. niger were collected from the four locations during January to December 2020. LFD analysis indicates three length classes 21-27 cm, 30-32 cm and 35-37 cm, respectively. This species showed isometric growth pattern (b = 2.981) that indicates that the size and weight increases proportionally and the surrounding habitat provides favourable environment for the growth. LWR between TL and BW were highly correlated (r² = 0.951). LLRs also showed significant correlation between TL and SL (r² = 0.845) and TL and FL (r² = 0.861). The mean value of KF was found as 1.60 which indicates that the BoB provides healthy environment for this species. The mean value of WR (101.09) indicates that the relationship between prey and predator was in balanced condition. This study suggests optimum catchable length for P. niger at 27 cm. Therefore, these findings could provide important information to design effective conservation and management planning for this species.

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