The selection of aerators and correct numbers can play an essential role in reducing the cost of production in aquaculture. The new generation aerators, namely spiral leaf, air‐jet, submersible and impeller, used in aquaculture, were assessed for its aeration efficiency and energy cost compared with the commonly used paddle wheel aerator. Of the aerators tested, the impeller had the highest aeration efficiency of 2.098 kg O2/kW hr, followed by paddle wheel with 1.436 kg O2/kW hr at 20‰ salinity. The spiral and air‐jet aerators had maximum aeration efficiency of 1.326 and 1.419 kg O2/kW hr, respectively, at 35‰ salinity. The submersible aerator was not efficient as its maximum efficiency was 0.380 kg O2/kW hr. The water flow by paddle wheel was 3 ft/sec and also provides better coverage than other types of aerators. The efficiency of aerators was high in optimum salinities (20‰ and 35‰) than the low or high saline condition. The average energy cost of shrimp pond aeration per hectare was lowest for impeller, followed by paddle wheel aerator. The study provided economic comparisons of vannamei culture using different aeration systems by keeping a uniform set of economic assumptions. Shrimp farms with impellors can give 14%–25% high returns across salinities, whereas spiral leaf can provide 5% high returns at 35‰ salinity. The combination of the type of aerators and the calculated use based on the salinity of the culture systems can result in energy‐saving and also a reduction in the production cost.

Journal of Environmental Biology Interpretation :The present study aimed at evaluating probiotic bacterial cells, Lb. rhamnosus by coating on seabass fish meat chunks against its spoilage indices,native and specific fish spoilage bacteria.Seabass fish fillets were cut into chunks, washed and taken into petri plates. Scores were made using sterile blade. Lb. rhamnosus cells were coated on the chunks using micro pipette and tested for antagonism against fish-borne specific spoilage bacteria such as Shewanella putrefaciens and Pseudomonas fluorescens through "Deferred antagonism assay". Spent culture of Lb. rhamnosus was assayed for antagonism through "Agar-well diffusion assay". The changes were estimated for two days following "Conway micro diffusion" method.

The use of antibiotics in aquaculture can prevent certain diseases, however, its use is highly restricted due to several environmental and human health problems like development of antibacterial resistance. Probiotics are widely used for improving production of aquatic animals by means of improving water quality as well as by nutritional and immune modulation in animals thus, helping in preventing diseases. The present study was aimed to evaluate different strains of probiotics viz., a commercial probiotic, Bacillus subtilis, Enterococcus sp., Lactobacillus casei, Lactobacillus rhamnosus, Saccharomyces cerevisiae and Saccharomyces boulardii on the growth, microbial load and immunomodulatory performance of the Pacific white shrimp, Penaeus vannamei. Seven probiotic feeds each containing 5 x 10 9 CFU ml -1 of respective probiotics kg -1 of feed were prepared by top coating on a pellet feed containing 35% protein and duration of the experiment was 75 days. All of the 6 selected strains of probiotics except the commercial one influenced the growth significantly when fed to the shrimp, compared to control group. Specific growth rate (SGR), average daily growth (ADG) and survival rate were observed to be higher in probiotic fed groups. Maximum growth was recorded in S. cerevisiae fed groups (8.05±0.21 g), followed by B. subtilis (7.65±0.21 g), while the control animals showed an average growth of 4.85±0.49 g with percentage improvement in the range of 50-95% when compared to all other treatments. Total heterotrophic count significantly (p<0.05) increased in the rearing water of B. subtilis treated group (8.995± 0.021 x 10 3 cfu ml -1 ) when compared to that of control (5.475± 0.003 X 10 3 cfu ml -1 ) and total vibrio load was greatly reduced in B. subtilis (1.42 ± 0.04 x 10 3 cfu ml -1) and S. cerevisiae (1.47 ± 0.01 x 10 3 cfu ml -1 ) treated water compared to control (4.265 ± 0.06 x 10 3 cfu ml -1). Non-specific immunity in terms of total haemocyte count (THC) was found to be significantly (p<0.05) higher in B. subtilis (12.4±0.8 10 6 cells ml ) treated groups. The probiotic effect was found to be beneficial for better growth and immunomodulation, which was however found to be strain-specific.

Polychaetes are multi‐segmented worms, being exploited from the backwaters for shrimp hatcheries to be used as a maturation diet for shrimp broodstocks. Non‐selective collection of polychaete worms poses a severe hazard to the ecosystem; hence, a grow‐out system was developed for Marphysa gravelyi. Adult, M. gravelyi of 17 ± 0.4 cm length (n = 40) when reared in 100 L tanks, produced 1800 numbers of juveniles having an average length of 7 ± 0.2 cm with 80% survival in 4 months. The juveniles (7 ± 0.2 cm (n = 50) worms were reared again in 25 L tubs from which 45 adults (20 ± 0.3 cm) could be produced in 4 months with 90% survival. Juvenile, M. gravelyi (n = 500) when mass‐reared in 1000 L FRP tanks by feeding Skeletonema costatum (106​ CFU/ml), produced 400 adults (20 ± 0.2 cm) as biomass with 80% survival in 4 months. The nutrient profile of adult M. gravelyi revealed protein, carbohydrate and lipid to be 33, 14 and 40 g % respectively. Crude M. gravelyi extract showed the highest bacterial inhibition on Staphylococcus aureus (18 ± 0.3 mm) and lowest on Bacillus subtilis (14 ± 0.2 mm). The present study revealed that growing polychaete worms in a controlled condition is advantageous, compared to collection of polychaete worms from wild which might seriously deplete their natural stocks, and cause physical disturbance of soil exposing heavy metals with the release of ammonia, and phosphorus compounds leading to eutrophication.