Suckermouth armoured catfish (Pterygoplichthys spp.) which is popularly called "Devil fish" in Andhra Pradesh, was recorded in 93.33% of fish ponds out of 600 ha surveyed in Krishna and West Godavari districts including mesohaline ponds wherein salinity ranges from 2 to 20‰. Pterygoplichthys spp. have ranged from 150 to 600 kg/ha that accounts to 2.01-7.50% of total biomass of fish harvested in aquaculture ponds leading to escalation of feed conversion ratio by 25.76%. Consequently, carp production has diminished by 18.88% to 22.92% leading to economic losses to fish farmers up to 13.40%. Food chain disruption by this alien fish is not only confined to benthic algae and periphyton but also foraging on supplementary feeds leaving primary fishes deprived from availing feed. Abundance of Pterygoplichthys spp populations in culture ponds as also in canals was high in monsoon season when compared to winter. Invasion and abundance of Pterygoplichthys spp in various river systems in Andhra Pradesh has become major concern for fishers causing extensive damage to nets and gears as also retarded catch per unit effort resulting in minimization of their income by 30%. Efforts to extract fish hydrolysate from Pterygoplichthys spp were futile due to intense bony skeleton and poor recovery rate which projected utilization of this fish for allied activities to minimum. Abundance of Pterygoplichthys spp is increasing in confined and open water bodies due to their tolerance and ability to grow and breed in variety of aquatic habitats including polluted environments as also lack of effective predators thus poses a high risk and threat to native freshwater species in any ecosystem in which they get established.

In spite of vast diverse fish genetic resource of India, several exotic species have been introduced into India. Chinese carps which were introduced in India with an objective of increasing the yields in aquaculture has paved way for composite fish culture in India. Introduction of exotic species for fisheries and aquaculture was successful in some instances while in few situations, it failed leading to controversy over protection of native biodiversity. Pangasius (Pangasianodon hypophthalmus) an exotic species has been introduced into India and is not only adopted for culture in states like West Bengal and Andhra Pradesh but also established as an alternative candidate species in freshwater aquaculture. Fish seed production segment in West Bengal played a pivotal role in the expansion of Pangasius farming in Andhra Pradesh. Pangasius monoculture was found to be profitable in comparison to polyculture with carps and other fishes. Use of formulated feeds is the major choice of Pangasius farmers. Pangasius catfish is less prone to diseases when compared to carps and is sensitive to abiotic stress. Comparatively, low market value of Pangasius than carps has increased avenues of fish consumption by low income consumers. Very fast development in culture of Pangasius has created many challenges such as dearth of quality seed, inconsistent management practices, prevalence of stress induced diseases, glut in the market and acute decline in the farm gate price leading to stabilization of farming area in Andhra Pradesh. Pangasius farming in Andhra Pradesh is sustaining due to strategic stocking and harvesting pattern adopted by the farmers conforming to market trend. Inappropriate practices in order to achieve higher yields and input-specific technical inefficiency are associated with the economic losses while minimizing the use of inputs can reduce risk factors in Pangasius farming. It is important to record that demand for carp culture in Andhra Pradesh is still greater in spite of less complications underlying in Pangasius farming and management.

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The present study was designed to demonstrate the seasonal variations in physico-chemical parameters in sh ponds and carried out for one year at monthly intervals in ten sh ponds. Maximum value of Gross Primary Production (GPP) and Net Primary Production (NPP) is observed during pre-monsoon and subsequently the lower values during monsoon season correspond to the attenuation of light. A signicant variation in seasonal community respiration was noticed during the study period. Seasonal uctuations in gross and net primary production values were quite apparent in surface waters and showed a bimodal type of distribution. The values were generally high during post winter months (March to June) and low during winter (January) and monsoon months (July and August). The dissolved oxygen content and chlorophyll-a were correlated with increase in temperature and light transparency during the pre-monsoon period whereas the phosphate concentrations were measured maximum in monsoon followed by pre-monsoon and post-monsoon suggested the accumulation of inorganic nutrients through terrestrial catchments