Brackishwater/Coastal Aquaculture

Coastal Aquaculture production in the country largely on account of shrimp farming is estimated that out of about 1.23 million ha identified as potential areas for brackish water fish farming in the country, Of the total area, about 10% area is being farmed at present. Of this area, about 80% is under traditional farming systems and the remaining is under extensive and semiextensive shrimp farming. The activities of shrimp farming on commercial scale are taken up in the states of Andhra Pradesh and Tamil Nadu. The traditional farming systems are located in West Bengal and Kerala. Commercial shrimp farming is more than a decade old in India and both shrimp seed production and farming practices are based on technology imported mainly from South-east Asian countries.

Fertilizer management in brackishwater aquaculture

Soil and water quality for brackishwater aquaculture is almost similar to freshwater aquaculture except water salinity. Salinity represents the quantity of dissolved salt in a given unit of water, and is usually expressed in g/kg of water (ppt). In brackishwater ponds salinity usually ranges between 0.5%0and 30%0depending on the distance from sea and seasonal variation due to monsoon precipitation.

Importance of changing water salinity on natural food production was studied by scientists and favourable range for growth and reproduction of many bottom flora and fauna has been identified. The effect of salinity on the growth and availability of fish food organisms may be due to its direct influences on the physiological process or due to its effect on the transformation of nutrient elements. The effects of different degree of water salinity on the transformation of nutrient elements and decomposition of organic matter in brackishwater ponds have been studied.

Most of the brackishwater species of commercial importance are euryhaline in nature which is related to their osmoregulatory adoptions. However, effect of salinity on the survival and growth of Penaeus monodon has been studied widely for its importance in global market. Though it is euryhaline in nature, high mortality and poor growth rate were found at salinities lower than 10%0.The salinity which supports normal growth of P. monodon is between 15 and 30%0.However, P. monodon could also survive and grow well at lower salinities and could tolerate freshwater for 30 days.

Culture fisheries resources of brackishwater sector in India surpass in magnitude those pertaining to freshwater ponds. However, in comparison to freshwater sector, production in brackishwater fish ponds is comparatively low. Lack of presence of sufficient fish food organisms has been considered to be one of the major reasons for such low productivity and to increase the productivity use of fertilizers and manures has been suggested. Benthic algae form the principal food item for all the non carnivorous brackishwater fishes and prawns. These algae grow on the surface of the bottom soils and derive their sustenance either directly from the soil or from the soilwater interphase. The concentrations of nutrient elements in either case are governed largely by the amount of water soluble and exchangeable ions present in the surface layer of the bottom soils. Considering this phenomenon, fertilization of brackishwater fish ponds is radically different in concept and practice from that of freshwater ponds. Since the purpose of fertilizing brackishwater fish ponds is to increase the growth of benthic algae, fertilizers in such culture system should be applied at the bottom of the ponds. Response as well as behaviour of different pond fertilizing materials in brackishwater ponds, therefore, depends largely on their transformation in the pond soils. Besides, widely changing water salinity levels of brackishwater fish ponds also contribute to availability of nutrient elements in such cultures.

(Source:Hand book of Fisheries and Aquaculture. 2006. Indian Council of Agricultural Research. New Delhi.)