Shrimp Pond Waste Management – Approaches
Increase in food production from fisheries sector led to introduction of noval technologies and intensive farming methods in shrimp culture that result in increased production of shrimp. Management of water and waste that produced is critical factor that has to be considered. In order to discharge waste water, some improved recirculating systems have been developed. But, the sludge has been neglected and posing a serious problem. So a systematic waste management strategy is needed which include treatment, disposal and recycling for a sustainable shrimp farming management.
Design and type of pond, culture system, and pond management method and pond inputs are criteria on which the distinctive nature of sludge or shrimp pond waste dependent. Naturally shrimp pond waste have higher content of organic matter, total nitrogen and phosphorous than normal soil and also high Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD).
Impact of Pond waste on shrimp culture
Growth and survival of the shrimp and quality of pond water is greatly affected with pond waste. Removal of sludge frequently from the pond bottom reduces the organic nutrients in water, which in turn affects the growth of phytoplankton; significantly pond productivity. The growth of Penaeus monodon fry has shown a negative correlation with ammonium and sulfide concentrations of sediment. In P. setiferus culture ponds, the shrimp survival and production has been shown to be very low in ponds with no to moderate removal of sludge during culture period.
Leaving sludge without removal may lead to accumulation in pond that not only increases sediment oxygen demand but creates anaerobic conditions resulting in undesirable gas production such as hydrogen sulfide. Large volume of accumulated shrimp pond waste will increase oxygen demand and cause oxygen depletion on the bottom that stress shrimp and subject them more susceptible to disease. The undesirable gases produced from pond waste can affect the appetite of shrimp increasing feed conversion ratio and leading to deterioration of water quality.
Effect of Pond waste on Environment
Shrimp pond waste management practiced during culture operation and post culture period reflects the degree of impact intensity of pond waste on the environment. The sludge from the shrimp farming industry on environment can be classified into three divisions.
– Impact on coastal water quality and hydrology.
– Impact on aquatic organisms, and
– Impact on mangrove and terrestrial vegetation.
Impact on coastal water quality and hydrology
Disposing shrimp pond waste into nearby aquatic environment increases nutrient availability promoting the growth of phytoplankton, thus leading to Eutrophication of the aquatic body. So pretreatment of pond waste before disposal is highly recommended.
Impact on aquatic organisms
Shrimp pond waste contains numerous suspended solid particles which cause turbidity in the receiving water. It has been reported that suspended solids are as high as 4200 mg/L from plastic lined intensive shrimp ponds. Turbidity in water reduces light penetration, thereby decreasing photosynthetic activity and dissolved oxygen level causing stress to aquatic organisms especially bottom dwelling animals. Presence of nitrogen and phosphorous in high amounts contributes to eutrophication in ponds.
Impact on Mangrove and Terrestrial Vegetation
Shrimp pond waste has positive impact on mangroves, for example pond waste (75%) and soil (25%) increases the growth of Rhizophora mucronata, R. apiculata and Bruiera cylindrica. However, overloading of pond waste should be avoided as this may cause mortality due to lack of respiration by mangroves pneumathodes. Many farmers also reported that better growth of mangrove was seen in area where dried shrimp pond waste was dumped. Applications of pond waste to terrestrial vegetation show negative effect as the concentration level of salts are high. The characteristic of shrimp pond waste differ with pond water quality, rainfall and pond inputs. Higher salinity in pond water results higher content of salts in shrimp pond waste.