Role Of Three Freshwater Shellfish In Reducing The Heavy Metal Content In Fish Farming

With the development of industry,agriculture and urbanlization,the pollution of heavy metal in water is becoming more and more serious,which makes the phenomenon of excessive of heavy metals in aquatic products and have potential harm to human health.How to repair the damaged aquaculture environment,reduce the content of heavy metal in aquatic products and ensure “safety of every bite of food” has become the focus of attention.Based on the above reasons,the fish,silver carp(Hypophthalmichthys molitrix),grass carp(Ctenopharyngodon idellus),black carp(Mylopharyngodon piceus)and crucian carp(Carassius auratus),were cultured in such conditions that the content of heavy metal(copper,zinc,cadmium and lead)in sediment of this study were reached or exceeded those in Xiangyin segment of Xiangjiang river to explore the migration and transformation of heavy metals in aquaculture water and aquatic products.The complex ecological method(freshwater shellfish-lime)was used to explore the role of reducing heavy metal content in cultured fish.The rusults are as follows:Compared with T1(heavy metals exceeded sediment),shellfish in T2(heavy metals exceeded sediment + free-range shellfish)and T3(heavy metals exceeded sediment + cage cultured shellfish)can reduce the heavy metal content in the aqueous and suspended solids,and the joint effects with quicklime is better.When confronted with heavy metal contaminated sediment,heavy metals in water are mainly present in suspended solids and sediments,and their contents was fluctuated under biological and human disturbance.Shellfish did not reduce the content of heavy metals in the sediments,and the contents of heavy metals in the sediments increased significantly(P <0.05)with the continuous input of the fodder.The different culture methods makes the heavy mental content in shellfish,Hyriopsis cumingii,Corbicula fluminea and Bellamya spp,appeared significant difference(P<0.05).Whether suspension farmed or free-range,the content of copper and cadmium in the soft part of H.cumingii decreased with the increase of body weight.The content of zinc and lead in the soft part of H.cumingii increased with the increase of body weight in the case of free-range,while suspension farmed was the oppsite.There was no significant difference in the contents of heavy metals among the same species of fish in T1,T2 and T3(P>0.05).Four species of fish in control(C,normal sediment)and treatment groups(T1、T2 and T3)was artificially divided into three parts: back muscles,"debris"(bone,fin,brain,scales,heart,abdominal muscles,and the rest of the back muscles)and "discarded"(hepatopancreas,kidney,maw,gall bladder,bowel and gill),and the content of heavy metal was reduced by used of quicklime two times a month,however,the application of quicklime four times in one month was the opposite.The contents of heavy metals in the demersal fish(crucian carp and black carp)were higher than those in the pelagic fish(silver carp and grass carp),and the fish,living in the condition of heavy metal excessive sediment(T1,T2 and T3),have higher content of heavy metal than the control group.The contents of four heavy metals in fish from high to low order of Zn > Cu > Cd > Pb,and it decreased with the increase of body weight.The order of the heavy metals contents in the back muscles,"debris" and "discards" were: "discards" > "debris" > back muscles.During 120 days of culture process,the contents of lead and cadmium in the back muscles of the four fish were not detected,and only the contents of lead and cadmium in the “discards” were higher than the limit of NY 5073-2006 and GB 2762-2012.