This study was designed to elucidate the effects of arsenic (As) on the morpho-behavior, growth development and molecular mechanisms of a commercially important fish, rohu carp, Labeo rohita, in Bangladesh. Fish fry with an average weight of 387.5 ± 169.25 mg and an average length of 3.35 ± 0.37 cm were collected from a local hatchery in Mymensingh, Bangladesh and acclimatized for a week in the Department of Fisheries, University of Dhaka before starting the exposure with arsenic. Fishes were exposed for a period of 14 days with three treatments of NaAsO₂, namely treatment 1(T1)—2.5 mg/L; treatment 2 (T2)—15 mg/L; and treatment 3 (T3)—30 mg/L, along with a control (C)—0.0 mg/L, with three replicates. These concentrations were determined based on the LC₅₀ value for 96 h measured for this experiment. This study revealed remarkable morphological abnormalities and deformities in arsenic-exposed rohu carp. In fish exposed to 30 mg/L, caudal fin erosion was a frequent deformity. There was no significant difference in RNA:DNA ratio among the treatments. The overall weight of fish was decreased as the concentration of arsenic was increased. The T3 fish had a statistically significant negative weight gain (−0.05 ± 0.07 g), but the other treatments (T1 and T2) and control fish had no significant weight gain. Different types of histopathological changes were observed in the gills and intestines of arsenic-treated fish. Necrosis and severe damages were found in the secondary lamellae of gills at the highest arsenic concentration (30 mg/L). Epithelial lifting, irregular shape and damages in the gill raker were also observed in the primary lamellae of the gills for the same treatment. In this study, the expression of heat shock protein (HSP 60) and metallothionein (MT) genes was assessed by qPCR, and these genes were upregulated in different treatments compared to controls. The findings of the present study suggest that arsenic pollution significantly changes the morphology, behavior, growth, development, histopathology and molecular mechanisms of this economically important fish, rohu carp, in Bangladesh.

Shrimp aquaculture has become a vital industry, meeting the growing global demand for seafood. Shrimp viral diseases have posed significant challenges to the aquaculture industry, causing major economic losses worldwide. Conventional treatment methods have proven to be ineffective in controlling these diseases. However, recent advances in RNA interference (RNAi) technology have opened new possibilities for combating shrimp viral diseases. This cutting-edge technology uses cellular machinery to silence specific viral genes, preventing viral replication and spread. Numerous studies have shown the effectiveness of RNAi-based therapies in various model organisms, paving the way for their use in shrimp health. By precisely targeting viral pathogens, RNAi has the potential to provide a sustainable and environmentally friendly solution to combat viral diseases in shrimp aquaculture. This review paper provides an overview of RNAi-based therapy and its potential as a game-changer for shrimp viral diseases. We discuss the principles of RNAi, its application in combating viral infections, and the current progress made in RNAi-based therapy for shrimp viral diseases. We also address the challenges and prospects of this innovative approach.

The effect of stocking density on growth of zebra fish was examined. Total five different stocking densities (5, 15, 25, 35 and 45 individuals per 2 liters of water) were maintained in triplicate for a period of 60 days. One month old zebrafish were randomly stocked into 15 tanks and fish were fed with commercial diet. The mean weight gain, specific growth rate and length gain for treatment 1 (5 fish/2liter) and treatment 2 (15 fish/2 liter) were significantly (p < 0.05) higher than treatment 3 (25 fish/2 liter), treatment 4 (35 fish/2 liter) and treatment 5 (45 fish/2 liter). The gender weight gain, survival rate and condition factor did not show any significant (p > 0.05) difference among treatments. The result of this study suggests that the stocking density of zebrafish could be 15 fish per 2 litre of water in a laboratory system with aeration.Bangladesh J. Zool. 44(2): 209-218, 2016

Effect of rearing density (5, 15, 25, 35 and 45 fish/l2) on reproductive performances such as spawning success, fertilization rate, hatching rate and embryogenesis in terms of per cent survival rate of embryos at cleavage, gastrula, segmentation, pharyngula and hatching were evaluated. Survival, hatching, fertilization rate and per cent survivability of embryos did not differ significantly between the treatments 1, 2 and 3, but showed significant difference (p < 0.05) between 4 and 5. Treatment three (25 fish/l2) had five-folds higher number of successful progeny than treatment one. Results suggest that 25 fish/l2 can be used as optimum rearing density. Dhaka Univ. J. Biol. Sci. 26(1): 77-82, 2017 (January)

Morphological and genetic diversity of three wild zebrafish populations in Bangladesh (Rangpur, Netrokona, and Cumilla) were elucidated using DNA barcoding and Random Amplified Polymorphic DNA (RAPD). Morphometric variation was minimal therefore, RAPD profiling and DNA barcoding were also used. Total 236 bands, including 29 polymorphic bands and 2 unique bands in RAPD showed 14.09% polymorphism indicating a low genetic diversity among them. Genetic distances were ranged from 0.0048 to 0.1031, with the highest genetic distance between Rangpur and Netrokona populations. DNA barcoding showed 99% similarity to Danio rerio from the GenBank, and multiple sequence alignment confirmed high genetic similarity (99.41) among these populations. Phylogenetic analysis showed these three zebrafish populations were grouped into distinct clusters, supporting the presence of genetic structure across populations. These information provides an essential reference data for the conservation, management, and potential selective breeding of zebrafish. The findings of this research also emphasize the efficacy of DNA barcoding and RAPD as complementary methods in the study of population genetics.

Complete mitochondrial DNA genome annotation of an ecologically and commercially important fish species Cirrhinus cirrhosus was executed with next-generation sequencing (NGS) for nucleotide and phylogenetic analyses. The findings of this study showed that the Cirrhinus cirrhosus mitochondrial genome contained 16,593 bp, including 13 protein-coding genes, 2 ribosomal RNA genes, 22 tRNA genes, and a D-loop region. The overall base composition was 32% adenine, 25% thiamine, 16% guanine, and 27% cytosine. This mitochondrial DNA exhibits an AT biasness, with 56% AT content in its genome. Significant fluctuations were identified in the AT and GC skew values of the ND6 gene, indicating that the selection and mutation forces acting on this gene might be different from those acting on other genes. The Ka/Ks ratios of most protein-coding genes were less than 1, indicating very strong natural selection pressure. Phylogenetic analysis of Cirrhinus cirrhosus with Cirrhinus mrigala and Bangana tungting suggested a closer evolutionary relationship among these species, which might have shared a more recent common ancestor. It has been also found that the genera Labeo and Cirrhinus are not monophyletic.