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Seaweeds can play an essential role in controlling antibiotic resistance for bacterial diseases. Three extracts of two brown seaweeds Padina tetrastromatica and Sargassum ilicifolium were investigated as growth promoters and to provide immune protection against Vibrio parahaemolyticus. Extracts of the two seaweeds were administered at 2.5 and 5 g kg−1 with food for 45 days to Penaeus monodon juveniles. The maximum weight gain (6.28 and 7.08 g), specific growth rate (3.39 and 3.32%), and survival rate (78.45 and 82.45%) of the juvenile tiger shrimp were obtained at a dose of 5 g kg−1 with P. tetrastromatica extracted by methanol and ethanol, respectively; which was significantly higher than the other solvents and control group (p .05). However, the administration of 5 g kg−1 methanol and ethanol extract of P. tetrastromatica improved growth performance and the immune capacity of P. monodon by increasing their phenoloxidase activity, superoxide anion concentration, and resistance against V. parahaemolyticus.HIGHLIGHTS The maximum growth performance and survival of juvenile tiger shrimps obtained with Padina tetrastromatica extract at a dose of 5 g kg−1. The methanol extract of P. tetrastromatica and Sargassum ilicifolium had maximal antibacterial activity against V. parahaemolyticus. The administration of 5 g kg−1 methanol and ethanol extract of P. tetrastromatica improved growth performance and the immune capacity of P. monodon.

The bacterial population plays a crucial role in recycling the organic matter and metabolizing the toxic nitrogenous compounds under biofloc technology (BFT). The biofloc technology has been successfully implemented for several fish species, but not for shrimp culture in Bangladesh. The major objectives of this study were to determine the effects of stocking density on the growth performance of tiger shrimp Penaeus monodon under biofloc technology (BFT) rearing system using commercial probiotics and to investigate the abundance of total heterotrophic bacteria (THB) and vibrio-like bacteria (VLB) in different biofloc treatments and their water quality parameters. The experiment was conducted with three different stocking densities in three BFT tanks (2.5 × 2.0 × 1.0 m) with triplicate and three control tanks filled in clearwater. All these tanks were built with cement and can contain 5000 L of water. Visually healthy, disease-free P. monodon postlarvae (weighted 0.18 ± 0.02 g) were collected from a local hatchery and stocked in three different stocking densities, i.e., 400 PL/m3 (CW), 400 PL/m3 (BFT1), 450 PL/m3 (BFT2) and 500 PL/m3 (BFT3). Shrimps were fed four times a day with commercial feed (Biomer, 40 % crude protein) for 127 days. Significant differences (P < 0.05) in specific growth rate, food conversion ratio, and protein efficiency ratio of shrimp were found among the treatments and the control group. The overall final biomass in BFT1 (5.88 ± 0.12 kg m3) was significantly higher (P < 0.05) than that of other BFT groups and the control (3.40 ± 0.09 kg m3). The present findings showed that the biofloc technology with lower stocking density was reducing the total ammonia nitrogen, nitrite-N, and nitrate-N in water and significantly increased THB and reduced VLB populations.

The recent incidence of loose-shell syndrome disease (LSSD) in grow-out shrimp ponds appears to be a major problem in Bangladesh. Therefore, the aims of our study were (i) to observe clinical signs of LSSD to confirm its incidence and (ii) to identify the probable causative agents for LSSD in shrimp. Sampling was conducted randomly from five LSSD-affected ponds and three non-affected ponds near Bakkhali River; ecological parameters were measured. A total of 180 healthy shrimps were used for this experiment, where LSSD-affected shrimp extracts were either injected into the shrimps or mixed with water in the experimental tanks. Finally, microbial examinations were performed to identify the possible LSSD causative agents from the infected individuals. The total shrimp production was higher in ponds with healthy populations (185 kg/ha) than from LSSD-affected ponds (126–146 kg/ha); the survival rate of shrimp at harvest was significantly different (p

Size frequency and length–weight relationships (LWRs) for three cephalopods, Indian squid Photololigo duvaucelii, needle cuttlefish Sepia aculeata, and spineless cuttlefish Sepiella inermis were studied. Specimens were caught from the coastal waters of Bangladesh (Moheshkhali Channel and Sonadia Island) using both trawl and marine set bag nets. The maximum dorsal mantle length for the Indian squid, needle cuttlefish, and spineless cuttlefish was recorded to be 228, 135, and 82 mm, respectively. The estimated growth coefficient b was 1.377 for Indian squid, 2.504 for needle cuttlefish, and 1.979 for spineless cuttlefish. The growth coefficient for these three species indicated hypoallometric growth from this region. No information has been published regarding size frequency and LWRs for these three cephalopods from the coastal waters of Bangladesh. The results of this study will be useful for the management and conservation of squid fisheries from the Bay of Bengal.

The temporal distribution pattern of zooplankton communities was studied in coastal waters of the northern Bay of Bengal, Bangladesh, during a 1-year period of investigation (May 2014-April 2015). Throughout the investigation, a total of 38 zooplankton species were recorded, in details 22 holo-plankton and 16 mero-plankton species. Copepods (Acartia danae, Acartia tonsa, Cyclops biscuspidatus, and Canthocalanus pauper), amphipods (Grandidierella megnae), shrimps (Penaeus indicus and Penaeus merguiensis), Acetes (Acetes indicus), and mysids (Americamysis bahai) were the dominant zooplankton taxa. The maximum abundance of total zooplankton and species richness was recorded in monsoon season whereas abundance of holo-plankton and species diversity was recorded in winter. Multivariate analyses revealed that the temporal pattern of species distribution of zooplankton communities significantly differed among the four seasons. RELATE analysis signified that temporal variation in species distribution and community structure of zooplankton significantly correlated with ecological condition of water. Moreover, BEST matching analysis indicated that NO2-N along with salinity, rainfall, transparency, TDS, TSS and pH were the main driving forces for these temporal variations in species distribution and community composition of zooplankton communities. Finally, correlation analysis showed that species evenness and diversity significantly correlated with salinity, transparency and TDS. These results suggest that zooplankton distribution pattern might be shaped by ecological condition of water in such marine ecosystem and may potentially be used as bioindicators of marine water quality.

Among the various potential sources of renewable energy, biofuels are of most interest. Marine microalgae are the most promising oil sources for making biofuels, which can grow very rapidly and convert solar energy to chemical energy via CO2fixation. The fatty acid profile of almost all the microalgal oil is suitable for the synthesis of biofuel. In this research, fatty acid and lipid contents of Bangladeshi strains of marine microalgaeSkeletonema costatumwere performed. For this, the crude oil was extracted by Soxhlet extraction method, using three most common solvent systems, pure hexane and mixture of CHCl3 : MeOH (2 : 1) and hexane : EtOH (3 : 1) one by one. Highest oil recovery (15.37%) came from CHCl3 : MeOH (2 : 1) solvent system from dry biomass whereas the lowest (2.49%) came from n-hexane from wet biomass. The qualitative analysis of the extracted oil by GC/MS analysis revealed that it contained significant amount of myristic acid (C14:0), palmitic acid (C16:0), stearic acid (C18:0), and palmitoleic acid (C16:1). It also indicated presence of hexadecatrienoic acid, benzenedicarboxylic acid, oleic acid, arachidonic acid, eicosapentaenoic acid (EPA), 9-Octadecenoic acid methyl ester (C19H36O2), and so forth. The obtained fatty acid profile indicates high potentiality ofS. costatumspecies to be used as promising biofuel feedstock a little improvisation and substantially it can replace diesel in near future.