Heavy metals (HMs) are natural environmental constituents, but their geochemical processes and biochemical equilibrium have been altered by indiscriminate use for human purposes. Due to their toxicity, persistence in the environment and bioaccumulative nature; HMs are well-known environmental contaminants. As result, there is excess release into natural resources such as soil and marine habitats of heavy metals such as cadmium, chromium, arsenic, mercury, lead, nickel, copper, zinc, etc. Their natural sources include the weathering of metal-bearing rocks and volcanic eruptions, while mining and other industrial and agricultural practices include anthropogenic sources. Prolonged exposure and increased accumulation of such heavy metals may have detrimental effects on human life and aquatic biota in terms of health. Finally, the environmental issue of public health concern is the pollution of marine and terrestrial environments with toxic heavy metals. Therefore, because of the rising degree of waste disposal from factories day by day, it is a great concern. Pollution of HMs is therefore a problem and the danger of this environment needs to be recognized.

The antibacterial effect of oxytetracycline (OTC) on bacterial load, pathogen and possible development of antibiotic resistance in intestinal flora of apparently healthy Nile tilapia (Oreochromis niloticus) was investigated under laboratory condition. OTC, a broad spectrum approved antibiotic widely used in aquaculture, was fed to Nile tilapia through medicated diet at a rate of 2 g/ kg of feed for consecutive 7 days in treatment 1 (T1) and 30 days in treatment 2 (T2). Changes in physico‐chemical parameters of water were also recorded where pH and dissolved oxygen influenced bacterial load and coliform count respectively. At the start of the experiment, initial bacterial load in fish intestine was 1.61 ± 2.25 × 1010 cfu/g, which after OTC treatment decreased significantly (p < .05) to 3.06 ± 2.08 × 108 cfu/g on day 7 and 3.45 ± 4.46 × 107 cfu/g on day 30 when compared with the control group. Among the 10 bacterial genera identified in the intestine, 4 potential public health concern bacteria viz., Salmonella, Escherichia, Enterobacter and Staphylococcaus were predominant. There was a sharp increase in bacterial load on day 18 in T2 that may be attributed to the development of antibiotic resistance in intestinal bacteria. Antibiotic susceptibility test for isolates against seven antibiotics: amoxycillin, ciprofloxacin, co‐trimoxazole, erythromycin, gentamicin, nitrofurantoin and tetracycline using disc diffusion method revealed significantly increased resistance of Gram‐negative rods (p < .05) that possibly caused increased frequency of OTC‐resistant microorganisms. In conclusion, short‐ and long‐term exposure to OTC treatment affected the distribution of bacterial genera including pathogens in the Nile tilapia gastrointestinal tract and concomitantly influenced their antimicrobial resistance.

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Background and Objective: With changing pattern of culture practices in the coastal region of Bangladesh, the euryhaline giant freshwater prawn Macrobrachium rosenbergii has recently gained popularity among farmers of both semi-intensive and extensive culture systems to improve profitability. Since bacteria are the key player in aquaculture facilities governing health and quality of fish and prawn, comparative bacteriological analyses were undertaken to understand the suitable testing system of bacterial analysis for cultured freshwater prawn.Methodology: Both on-farm and laboratory conditions in low-resource settings were considered to monitor bacterial population in terms of bacterial count, gram staining and presence of enteric bacteria associated with prawn and its surrounding environment.Results: On-farm counting was about one log-unit lower total viable count in water, sediment and prawn samples compared to those of laboratory testing. The differences between on-farm and laboratory analysis probably occurred due to the time lapse during sample transportation. Study also showed that gram negative bacteria were dominant and enteric bacteria were present in both the prawn farms with more or less similar frequencies. Conclusion:It is concluded that the apparent difference in bacteriological condition of the two farms is possibly related to the differences in culture practices, environment and culture conditions and the study has recommended on-farm testing as an ideal bacteriological analysis method.