COMPARISON OF FOOD ORGANISMS IN GASTROINTESTINAL TRACT OF PADDLEFISH (POLYODON SPATHALA) AND BIGHEAD CARP (ARISTICHTHYS NOBILIS) FROM POND

Three consecutive analysis of gastrointestinal contents of paddlefish (Polyodon spathala) and bighead carp (Aristichthys nobilis) were conducted. To find out their natural food organisms and difference, the fishes were cultured in the same farming pond. The paddlefish and bighead carp were large size fingerlings propagated in this year from the same trail fishery. Two repeated ponds were prepared, and 14 paddlefishes together with 14 bighead carps were included in each pond. All fishes were fed with natural food in the ponds during the whole trail. Each three replicate samples of gastrointestinal tracts of two species of fishes were collected once for three times from the start of the experiment (3d, 11d and 19d). The identification of food organism was carried out with microscope in the lab. Firstly, the unweighted pair group method with arithmetic mean (UPGMA) cluster analysis was performed on the basis of food organisms identification in gastrointestinal tract of two fish species. The results showed the composition of food organisms was different in two fish species gastrointestinal tract at the same sampling time, they were grouped into different branches. Moreover, the species numbers of cladocerans and copepods in paddlefish gastrointestinal tract were more than that in bighead carp's at all sampling times. Meanwhile, the biomasses of food organisms in two fish species gastrointestinal tract were analyzed. The results showed that when cladocerans and copepods were rich in the pond, there was no difference for their biomasses in two fish species gastrointestinal tract (P 0.05); when cladocerans and copepods were lack in the pond, the feeding intensity of paddlefish declined, but the biomasses of cladocerans and copepods was still higher (P 0.05); however, when the cladocerans and copepods disappeared in the pond, the biomass of rotifer in paddlefish increased more (P0.05); in contrast, smaller food organisms were filtered by bighead carp in the different periods. In addition, more bioflocs had been filtered by two fish species as the animal food organisms becoming fewer and fewer. In conclusion, there was feeding competition pressure between paddlefish and bighead carp in the same pond, which was closely related to the larger prey richness in the pond.