M. Muralidhar

Acute Toxicity of Some Heavy Metals to Lates calcarifer Fry with a Note on Its Histopathological Manifestations

Abstract Static bioassay tests for acute toxicity of four heavy metals to fry of the fish Lates calcarifer in brackishwater medium were conducted. The 96 h LC50 values of metals such as Hg, Cu, Cr, and Mn for two different size groups 11 ± 3 mm and 24 ± 4 mm were found to be 0.085, 1.3, 27.9, and 220 mg/L and 0.20, 1.8, 33, and 250 mg/L, respectively. The rank order of toxicity of metals was found to be Hg>Cu>Cr>Mn. Using the safe concentration factor of 0.01, the allowable safe concentration for Hg, Cu, Cr, and Mn in brackishwater are 0.00085–0.002, 0.013–0.018, 0.279–0.33, and 2.20–2.50 mg/L, respectively. The damage caused to different organ systems of the fish, exposed to the heavy metals, agrees with the rank order of the toxicity. Heavy nerve tissue necrosis was observed in fish exposed to mercury. Copper induced gill epithelial necrosis and kidney tubular degeneration. Chromium and manganese accounted for various histopathological manifestations involving vital organs such as liver and kidney.

STUDIES ON THE USE OF NEEM PRODUCTS FOR REMOVAL OF AMMONIA FROM BRACKISHWATER

ABSTRACT Laboratory experiments were carried out to investigate the ammonia removal from brackishwater (Salinity 16 ± 1 ppt) using natural plant products such as seed powder and seed oil from neem (Azadirachta indica) and commercially available neem products—neemazal and neemgold. The experimental results showed that ammonia removal was effective with 90 mg/l of neem oil, whereas, neem seed powder at 90 mg/l registered an increase in ammonia levels throughout the course of the experiment. Neem oil, neemazal, and neemgold at 90 mg/l were effective in decreasing the total ammonia nitrogen (TAN) level of 0.40–0.45 mg/l in 96 h. The effect of initial ammonia concentrations on the ammonia removal using neem oil revealed that percentage ammonia removal decreased with an increase in initial ammonia concentration.

Water Quality Management in Fish Hatchery and Grow-Out Systems

Aquaculture in India with its immense potential in marine, coastal and brackish water resources is expected to contribute significantly in protein-rich fish food, rural employment and utilisation of water resources and wastelands. Brackish water aquaculture, which made quantum jump in the 1980s, had to face a setback in the second half of 1990 due to the uncontrolled disease outbreak. Diversification of species has become unavoidable to sustain the aquaculture. The logic for introducing different alternative species in aquaculture system is that the intensity of the pathogens dependent on a particular host will be reduced and the consequent problems will get reduced. In this context, for India, many finfish like Asian sea bass, grouper, milkfish, cobia, pearlspot, pompano, etc., are considered as suitable alternative fish species farming in all the culture ecosystems. To have adequate amount of quality seed, there is a need to set up fish seed production hatchery with suitable technology. As it is evident the good water quality will ensure the quality seed production, we need to have good water management in fish seed production cycle and in fish grow-out system (Bisson et al. 1992; Qin et al. 1995). This chapter will bring out the best way to manage water quality in a fish hatchery and grow-out system.

Nitrogen Assessment and Management in Brackish-Water Aquaculture of India

Abstract The synthesis of information on nitrogen dynamics in aquaculture ponds and coastal ecosystems indicates uncertainties in our understanding. Coastal water bodies receive external input of reactive N (Nr) from brackish-water aquaculture (BWA) ponds utilizing natural resources, such as land, water, and biological resources such as seed and feed. BWA pond soils contain comparatively lesser amount of available nitrogen compared to freshwater ponds. Nitrogen limits the primary productivity of ponds, and transformation of nutrients in pond soil depends considerably on the widely fluctuating water salinities during different seasons of the year. Nitrogen budgeting studies showed that only 25–30% of the feed N is recovered in the cultured animals at harvest and is the major contributor for deterioration of water quality through discharge water and lost to atmosphere as volatilized ammonia and production of greenhouse gas N2O. Improving N use efficiency through better management practices can reduce N2O emissions. Research on improvements in nitrogen utilization, data on species-level efficiency, and simultaneous reduction of nitrogen loss is highly desirable for sustainable aquaculture development.

Temporal and Spatial Distribution of Sulfate Reducing Bacteria in Shrimp Culture Pond Sediment

Sulfate reduction, a key process in aquatic sediments is carried out by a group of anaerobic microorganism called sulfate reducing bacteria (SRB). High numbers of sulphate reducers in shrimp aquaculture pond sediment deteriorates the soil and water quality, causing physiological stress, thereby reducing the immunity of cultured animal. An attempt was made to evaluate the temporal and spatial distribution of SRB horizontally at different locations viz., water pumping area (WPA), sluice gate (SG) and pond center (PC), and vertically from sediment water interface to 10 cm depth in Pacific white shrimp, Penaeus vannamei culture ponds. Physico-chemical characteristics of water and soil were correlated with the number of SRB. Distribution of SRB was significantly higher (p ≤ 0.05) in the pond sediment nearer to SG (874 MPN/g), followed by PC (272 MPN/g) and WPA (99 MPN/g) and at sediment water interface (751 MPN/g) compared to 10 cm depth (114 MPN/g) of Original Research Article Thulasi et al.; AJEE, 3(4): 1-16, 2017; Article no.AJEE.35287 2 pond profile. Factors like dissolved oxygen and soil redox potential (oxidation to reduction scale), and organic carbon content in soil had a significant negative and positive correlation with SRB numbers. Phylogenetic relationship of SRB targeting SRB groups showed the presence of Desulfonema, Desulfosarcina, Desulfatibacilum, Desulfobotulus, Desulfomicrobium, Desulfococcus, Desulfovibrio and Clostridium genera in shrimp culture pond sediments.

Antibacterial efficacy of zinc oxide (ZnO) nanoparticles on Vibrio anguillarum

Vibriosis is the most prevalent bacterial disease which causes high mortality among aquatic animals. Vibrio anguillarum is one of the main causative agents of Vibriosis. In the present study to control V. anguillarum, ZnO nanoparticles with average size of 50nm were synthesised using varying concentrations of starch (0.1%, 0.5% and 1%) as stabilising agent. Minimum inhibitory concentration (MIC) of the synthesised nano-ZnO was determined and compared with that of commercial nano-ZnO of 50 nm. Results showed that nanoparticles had varying antibacterial activity on V. anguillarum and nano-ZnO synthesised using 0.5% starch had the most efficient antibacterial activity against V. anguillarum with a MIC of 30μg/ml. The results concluded that nano-ZnO is an effective bactericidal agent against V. anguillarum.