Size dependent ingestion and effects of microplastics on survivability, hematology and intestinal histopathology of juvenile striped catfish (Pangasianodon hypophthalmus).

Microplastic pollution is drastically increasing in aquatic ecosystems and it is assumed that different sizes of microplastics have diverse impacts on the physiology of aquatic organisms. Therefore, this study was intended to examine the ingestion and size specific effects of polyamide microplastic (PA-MP) on different physiological aspects such as growth, feed utilization, survivability, blood parameters and intestinal histopathology of juvenile striped catfish (Pangasianodon hypophthalmus). In a 28-day exposure, the fish were fed with different sized PA-MP with a concentration of 500 mg per kg of feed in order to simulate highly microplastic contaminated environment. Three different treatments were set for this experiment i.e. T1, 25-50 µm (smaller microplastic); T2, 300 µm-2 mm (larger microplastic); T3, (mixed) including a control (C); each had three replicates. The highest ingestion was recorded in the gastrointestinal tract (GIT) of fish exposed to smaller PA-MP treatments (T1 followed by T3). The results also showed compromised weight gain (WG; g), specific growth rate (SGR; %/day) and feed conversion ratio (FCR) with the exposure of PA-MP. Besides, survivability significantly reduced among treatments with the ingestion of smaller sized microplastic and found lowest in T1 (65.0 ± 5.0). In addition, the presence of PA-MP in feed negatively affected the concentration of hemoglobin and blood glucose. Similarly, smaller PA-MP caused most erythrocytic cellular and nuclear abnormalities; found highest in T1 that significantly different from other treatments (p < 0.05). Various histopathological deformities were observed in fish fed with PA-MP incorporated feed. The principal component analysis (PCA) showed that the toxicity and stress imparted by smaller PA-MP affected the survivability and blood parameters where larger PA-MP caused mild to severe abnormalities. Based on eigenvector values, the major abnormalities in intestine included occurrence of epithelium columnar degeneration (ECD: 0.402; PC1), hyperplasia of internal mucosa (HISM: 0.411; PC1), beheading of villi (BV: 0.323; PC1), atrophy of mucosa (AM: 0.322; PC1), tiny vacuoles in apical villi (TV: 0.438. PC2), crypt degeneration (CD: 0.375: PC2) and atrophy of goblet cell (AGC: 0.375; PC2). Therefore, it has been speculated that the size based PA-MP ingestion in the GIT interfered with the digestion and absorption as well as caused deformities that reflected negatively in survivability and hemato-biochemical parameters of juvenile striped catfish.

Effects of probiotics on growth, survival, and intestinal and liver morphometry of Gangetic mystus (Mystus cavasius).

The usage of probiotics proved advantageous in aquaculture due to its positive impact on fish growth, immune response and environment. This study was aimed to assess the effects of probiotics on growth, survival and histometry of intestine and liver in Gangetic mystus (Mystus cavasius) using two separate experiments for a period of 8 weeks (in aquaria) and 16 weeks (in earthen ponds). Three different probiotic treatments were incorporated i.e. commercial probiotic one; CP-1 (T1), commercial probiotic two; CP-2 (T2), Lab developed (Lab dev.) probiotic (T3) including a control. The results indicated that the probiotics usage especially Lab dev. probiotic (T3) significantly improved the growth parameters such as weight gain (g) and specific growth rate (SGR, %/day) as well as ensured better feed conversion efficiency. Zero mortality was observed in aquaria whereas probiotic application enhanced survivability in earthen ponds. Moreover, all probiotic treatment exhibited positive results for different histo-morphometric features of intestine and liver. Mucus secreting goblet cells and fattening of mucosal fold increased significantly with probiotic usage. The amount of regular shaped nucleus was maximum in T3 with least intra cellular distance between liver tissues in earthen ponds. The greatest value for hemoglobin with lowest glucose level was observed in T3 as well. Furthermore, probiotic ensured low concentration of ammonia during culture. Overall, it was anticipated that the application of probiotics in Gangetic mystus culture resulted positive effect on its growth, feed utilization, survivability, histo-morphometry, immunity and hematological parameters.

Population parameters of the orange mud crab Scylla olivacea (Herbst, 1796) from the Sundarban mangrove forest in Bangladesh.

Population parameters of orange mud crab (Scylla olivacea) were estimated, aiming to determine sex ratios, carapace width-body weight (CW-BW) relationships, asymptotic width (CW∝), growth coefficient (K), mortality (Z, M, and F), recruitment and level of exploitation (E) in the Sundarban mangrove forest, located in the south-western part of Bangladesh. Year-round samples were collected using hook-lines and baited traps, the population parameters were measured from CW frequency data using FiSAT-II analyzer. The study showed that the overall male and female sex ratio was 1:0.66, revealing a male domination in the study area. The CW-BW relationship indicated that the increment rate in the BW of the male crabs (b = 3.06, R2 = 0.98) were higher than that of female (b = 2.62; R2 = 0.98) S. olivacea. The b value differed significantly (P < 0.006) from isometric growth (b = 3) where males exhibited positive and females exhibited negative growth allometry. Estimated CW∝ for male and female were 164 mm and 152 mm along with K values 0.90 yr-1 and 0.76 yr-1, respectively. Total mortality (Z) was 2.67 yr-1 and 1.57 yr-1, natural mortality (M) was 0.98 yr-1 and 0.90 yr-1 and fishing mortality (F) was 1.69 yr-1 and 0.67 yr-1 for male and female, accordingly. Recruitment of both sexes exhibited a bimodal recruitment pattern where young population occurs continuously throughout the year and a major peak of recruitment for males was observed from November to January and for female it was from February to April. The estimated exploitation rate (E) for male (0.63) was higher than the female (0.43) where the E for male exceeded the maximum permissible limit (E = 0.50). A remarkable range of fishing pressure at lower size classes was revealed in this study and thus framing minimum legal size is crucial for effective management of the population.

Taxonomic confirmation of mud crab species (genus Scylla) in Bangladesh by nuclear and mitochondrial DNA markers.

Taxonomy of mud crabs genus Scylla has been misidentified for several years due to their high morphological plasticity. Several reports concerning mud crab have been published with misleading identification in Bangladesh. In this study, partial fragments of nuclear and mitochondrial DNA of Scylla species obtained from four locations along the Bangladesh coast were used to resolve taxonomical ambiguity of mud crab species. A single PCR product from the nuclear first internal transcribed spacer (ITS-1) marker and phylogenetic trees constructed based on 16S rDNA sequences indicated that all Scylla species obtained in this study were S. olivacea. Both molecular data and morphological characters revealed that S. olivacea is the only major species in Bangladesh coastal waters. Further, the 16S rDNA haplotypes significantly differed with known S. serrata by 33%. From this study it is clear that 'S. serrata' commonly reported from Bangladesh should be S. olivacea.