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Fish culture aimed at high production through intense culture practices often leads not only to the alteration in water quality but also to severe disease problems. The accumulation of organic wastes deteriorates water quality and encourages the proliferation of pathogenic microorganisms. To avoid these problems, probiotics are used as bioremediation tool. The present study was aimed to know the changing patterns of beneficial and pathogenic bacterial loads and water quality in fish ponds treated with pond probiotics. For this study, three earthen fish ponds, were cultured Pangasius sutchi, Catla catla and Labeo rohita, located in Balliparru near Machilipatnam in Krishna District, Andhra Pradesh, India were selected and studied for a culture period during 2009 to 2010. Two ponds were treated with probiotics having Nitrosomonas (1.62 kg/ha) and Nitrobacter (0.82 kg/ha) species and one pond was kept as control. During the culture period (August 2009 to July 2010), water quality parameters and the populations of total heterotrophic bacteria (THB), beneficial bacteria (Nitrosomonas and Nitrobacter species) and pathogenic bacteria (Pseudomonas) in water were analyzed. It was observed that in treated ponds, THB and beneficial bacterial load increased and pathogenic Pseudomonas load decreased. The bacterial population changed during every fortnight sampling of the culture period. The changing patterns of different bacteria in treated and control ponds were compared and discussed. The concentrations of ammonia, nitrite and phosphates were observed to be low in treated ponds than in the control pond. The present study revealed that the probiotics are instrumental in maintaining good water quality, higher beneficial and lower pathogenic bacterial loads in fish ponds.

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Groupers (Perciformes: Serranidae: Epinephelinae) are a significant group of marine and estuarine fishes having ecological and commercial importance in tropical and subtropical waters. The genus Epinephelus is identified based on the color configuration and morphological characteristics. The homogeneity in the morphological characteristics has created confusion in the species identification of Epinephelus. Epinephelus areolatus with its delicious taste has high economic value; however, its population showed a remarkable decline in recent times due to overfishing. Due to morphological resemblance, it has often been confused with Epinephelus chlorostigma and Epinephelus bleekeri, which leads to misidentification. Hence, correct identification of species is needed for the proper management of fish resources. This study aims to identify and validate E. areolatus by using morpho-meristic characteristics, including the number and pattern of pyloric caeca, vertebrae count through radiograph imaging, scale and otolith morphology, and DNA barcoding. The morphological and meristic characteristics of Epinephelus species observed in Nizampatnam coast are strikingly comparable to those reported earlier as E. areolatus. Comparative molecular analysis was also carried along with other morphologically similar species, viz. E. chlorostigma and E. bleekeri, using mitochondrial cytochrome oxidase I gene sequences. The mean interspecific genetic distance revealed high similarity with E. bleekeri (0.109 ± 0.012) and low similarity with E. chlorostigma (0.079 ± 0.009). The neighbor-joining tree has shown distinct clades for three species with high bootstrap values. The partial DNA sequence of the mitochondrial cytochrome oxidase I was established for the first time for E. areolatus from the Nizampatnam coast in this study.