62 JUNE 2015 • WORLD AQUACULTURE • WWW.WAS.ORG reptiles, including Indian flapshell turtles. Four species of Eimeria (E. legeri, E. mitraria, E. triangularis and E. trionyxae) were identified in Indian flapshell turtles (Helke et al. 2006). Generally, Eimeria infection can cause destruction of infected cells and surrounding tissue, resulting in necrosis and hemorrhage and cellular infiltration and architectural change (Gardiner et al. 1988). Turtles are potential carriers of bacterial pathogens, nematode worms and parasites that may be transmitted to cultured fish and infect them, causing disease and subsequent mass mortality, and leading to production loss and infection of the end consumers of fish. Damage to cage culture nets. Turtles cut the netting of fish cages in lakes or reservoirs, which may create great nuisance. For example, farm-raised, non-native fish can create a potential nuisance if some of the fish escape through net openings created by turtles. Cage net damage may also cause production losses to the farmer due to reduced yield and overfeeding. Damage to hapas in nurseries. Nursery rearing and breeding of freshwater fishes (tilapia and Indian major carps) is done by placing net hapas in ponds. Freshwater turtles can cause damage of those net hapas, resulting in escape of larval fish and financial loss to nursery operators. Escaped larval fish can become prey of freshwater turtles. There are also more chances for non-native fish to enter natural water bodies. Competition for feed. Freshwater turtles in culture ponds compete with the aquaculture species for natural foods. Turtles also learn quickly to eat commercial floating and sinking feeds offered to aquaculture species. Because of the invasion of these turtles, cultured fish will not get sufficient feed because these turtles consume a considerable quantity of feed offered to aquaculture species. This will reduce the growth rate of fish, increase FCR and extend the duration of the culture period. Overall, the farmer will incur financial loss. Competition for space. Freshwater turtles inhabit culture ponds reducing carrying capacity substantially. The space occupied by turtles would be otherwise used by aquaculture species and contribute to production. Eradication Methods Grow-out culture ponds Bottom set gill net. Turtles can be caught with 40-mm mesh, fixed gill nets placed on the pond bottom and secured with poles made from casuarina or bamboo. The net should be fixed near the dikes of the pond at each side. Generally turtles leave the pond at night and will be entangled in a gill net fixed on its route. By the same way, turtles that are approaching the pond and crossing over the dikes also get enmeshed in the gill net. This is the best and simplest way to remove turtles from culture ponds. The fixed gill net may be kept for at least 10 days to completely eradicate turtles from the pond. Every morning the net is inspected, the caught turtles extracted and the net reset for additional turtle catches. This practice was experienced practically from the fish culture ponds in the Andhra Pradesh. About 64 turtles were caught in five days from a fish culture pond where the photographs were taken. Captured turtles were released into wild natural water bodies. This method should be practiced during the initial days of fish culture; otherwise, when the fish have grown, there is a huge area for fish to get entangled into the net set for turtles. Seining and partial fish harvest. Aquaculture farmers in Andhra Pradesh generally conduct partial harvests to reduce fish biomass by harvesting marketable size fish in the middle of the culture period and allow the remaining smaller fish to grow. Partial harvest by seining will also capture some of the turtles in the pond. These farmers safely transfer captured turtles to natural habitats away from the farm site and are not consuming the freshwater turtles. Hooking. Freshwater turtles are regularly preying upon commercial fish species (carps) during their earlier life stages in the aquaculture ponds. Hence, baited hooks are frequently used by fishermen for catching turtles. Trapping. Trapping is another practical and efficient method of removing turtles from an aquaculture pond. Submerged traps are suitable for catching soft-shell turtles (Fowler and Avery 1994). Although it is an effective method, farmers of Andhra Pradesh are not practicing this method. Manual collection. Rashid and Swingland (1997) observed turtles can be easily collected at night, when they approach pond banks in response to light. When turtles come out of pond to cross the dike at night, they can be collected manually by laborers or night caretakers of the pond by holding a light source to attract FIGURE 4. Protective crab fencing for control of turtle entry
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