Effects of co-cultured fish and feed supplement on water chemistry characteristics of freshwater pearl mussel farming

Abstract

Integrated culture is widely used in freshwater pearl mussel(Hyriopsis cumingii) farming;however,water chemistry characteristics relating to H.cumingii farming are poorly understood.To assess the effects of co-cultured fish(grass carp,gibel carp,silver carp and bighead carp or silver carp and bighead carp) and formu-lated fish feed supplement(with or without feed supplement) on water chemistry characteristics,a 155-day field experiment was carried out in land-based enclosures.Four treatments including GGSB-F(co-cultured fish grass carp,gibel carp,silver carp and bighead carp were fed formulated feed),GGSB-NF(co-cultured fish grass carp,gibel carp,silver carp and bighead carp were not fed formulated feed),SB-F(co-cultured fish silver carp,and bighead carp were fed formulated feed) and SB-NF(co-cultured fish silver carp and bighead carp were not fed formulated feed) were established.The results indicated that the combination of co-cultured fish species could significantly affect Ca2+,total alkalinity(ALK),total hardness(HT) and total phosphorus(TP),while the feed supplement regime affected Ca2+,ALK,HT,ammonia(TAN),TP and chemical oxygen demand(CODMn).Dis-solved oxygen(DO) and secchi depth(SD) were lower,while Ca2+,HT,total nitrogen(TN),TP,TAN and CODMn were higher in the GGSB-F enclosures.Conversely,DO and SD were higher,but Ca2+,HT,TN,TP,TAN and CODMn were lower,in the SB-NF enclosures.During the experimental period,Ca2+ decreased,while TN,TP,TAN and CODMn increased.DO and SD were positively correlated with each other and negatively to the levels of TAN,TN,TP,Ca2+ and CODMn.Therefore,water quality management programs should include controlling the concen-tration of TAN and CODMn at the levels below the critical values,and maintaining Ca2+ and DO at high and con-stant levels.