Target-specific feeding strategies in carp-tilapia polyculture ponds: Effects of feed type and carp size

In polyculture ponds, feeding strategies can affect the species-specific intake and utilisation of both supplementary feed and natural food, thereby influencing overall pond performance. This experiment tested the effects of two feeding strategies and two carp sizes at stocking in a two by two factorial design on fish performance and the food web in carp-tilapia polyculture ponds. The two strategies were feeding a low protein-floating feed in combination with a high protein-sinking feed (F L S H ) and a high protein-floating feed in combination with a low protein-sinking feed (F H S L ). The two carp sizes stocked were small (∼22 g) and big (∼135 g). Ponds with small carp were stocked with 144 carps, while ponds with big carp were stocked with 72 carps. Each pond was stocked with 16 similar sized tilapia. To give an equal nutrient input across all the ponds, the feed ration was determined for the small carp-ponds at the level of 18 g.kg −0.8 .d −1 , assuming 100 % survival. An equal amount of feed was applied to the big carp-ponds. The experiment was conducted in Bangladesh under very hot conditions associated with climate change: the average water temperature ranged between 33 and 35 ℃ in the afternoon (12:00–16:00 h). Results showed that the feeding strategy did not affect fish production and natural food availability (P > 0.05). However, survival was affected by feeding strategy (P < 0.05), carp size (P < 0.001) and their interaction (P < 0.05). Small carps, especially catla, suffered from higher mortality, but feeding a high protein-floating diet improved their survival. Despite lower survival and a higher body maintenance cost, ponds with small carps yielded a higher production than ponds with big carps. The underlying reason is possibly the stimulation of natural food production in the pond by the higher number of small fish present. • Varying the feed nutrient input into surface and bottom of the pond does not affect total or species specific production. • A high-protein floating diet helped catla to cope with unforeseen high temperature stress. • Pond production of a lot of small carps is higher than of a few big carps. • Catla and silver carp are more sensitive to high temperature than tilapia and rohu.