Effects Of Different Carbon/nitrogen Feeding Models On The Diet,edible Partial Nutrition Composition And Water Quality Of Rice-crayfish Co-culture System

The mode of rice-crayfish co-culture is an ecologically efficient new-technology culture mode that has emerged in recent years in China.Under the premise of ensuring grain output without reducing production,cultivate Procambarus clarkii in paddy fields which is established with ring ditch around.It is played an important role in improving the economic efficiency of farmers.At present,there is no relative systematic feeding mode for rice-crayfish co-culture mode,and the utilization of rice field resources by Procambarus clarkii is not clear enough.This study explored the diet of crayfish by optimizing C/N of feeding mode.Which is combined with the analysis of the nutrient composition of crayfish to provide some references for the design of a reasonable feeding mode.Through the detection of water qualit,a reasonable way to return straw was obtained,which provided a reference for the rational use of chemical fertilizers.In the rice-crayfish co-culture system,natural resources and primary productivity of rice fields are abundant,which provide abundant natural baits for crayfish.At present,there is no report about the utilization of rice fields with crayfish.In this paper,C/N was increased by adding carbon source to feed,which makes nitrogen utilization increase and enriches the density of natural baits in rice fields.We designed three feeding modes as group A(formulated diet C/N: 8),group B(formulated diet and bran C/N: 12)and group C(formulated diet,bran and glucose C/N: 16).Stable isotope techniques were used for analyzing the feeding habits of crayfish.The results showed that:(1)The ?13C and ?15N values of muscles in different dietary C/N groups were significantly lower than the juvenile crayfish muscle(P<0.5),and the ?13C values of adult crayfish muscle decreased with the increase of C/N.While the ?15N values of crayfish muscle in group B with different sizes were higher than the other two groups.In the same C/N treatment,the ?13C and ?15N value of crayfish muscle of a small size crayfish were the highest.(2)According to the analysis of diet,formulated feed was the first food source of crayfish with different sizes in group A,accounting for 38.03% ~ 44.17%.Formulated feed was still the first contribution of crayfish diet with different sizes in group B but dropped to 22.13% ~ 25.35%.In Group C,the organic debris for the diet of small size crayfish accounted for 19.93% is the first food source.Formulated feed was the first food source of middle and large size crayfish declined further to 18.85% and 19.4% respectively.The natural food proportions including zooplankton,algae and Alternanthera philoxeroides are significantly increased in groups B and C compared with group A.Based on the analysis of the edible rate,fullness,and nutrient composition of the edible part of Procambarus clarkii under different C/N feeding modes in the ricecrayfish co-culture cycle,the results showed that:(1)There was no significant difference between the hepatopancreas index,meat yield,fullness and total edible rate(P>0.05),while the hepatopancreas index of group B and group C females was significantly higher than that of group A(P<0.05).The gonadal index in group A was significantly higher than that in group B and group C(P<0.05).The females and males in group C had the highest meat yields,and group B had the highest fullness in females and males.Overall,the hepatopancreas index and total edible rate of females were higher than that of males,and males had higher meat yield and fullness.(2)There was no significant difference in the composition(P>0.05)of the normal biochemical composition of edible parts of female and male crayfish in each group except that crude protein content of female hepatopancreas were significantly higher in group C than in group B(P<0.05).The total lipid of the muscles and hepatopancreas of the females were higher than that of the males.Water content of muscle and hepatopancreas of the males and crude protein of the hepatopancreas were higher than that of the females.(3)The main saturated fatty acids in various female and male muscles were C16:0 and C18:0,except for C20:1n9 in group C male muscle,which were significantly higher than that in group B(P<0.05).There was no significant difference in fatty acid content(P>0.05).The polyunsaturated fatty acid n-3/n-6 in hepatopancreas of group A was higher than that in group B and group C(P> 0.05).The C18:1n9 in the hepatopancreas of group C males were significantly higher than that in group A and group B.The ?SFA,?MUFA,and ?PUFA in group B female hepatopancreas were significantly higher than those in group A and group C(P<0.05),and ? n-6PUFA were significantly higher than group C.(4)17 amino acids were detected in the muscles and hepatopancreas of each group of Procambarus clarkii,including 9 essential amino acids.The limiting amino acid of muscle were methionine and cysteine,and the essential amino acid score of muscle was higher than that of male.The total amino acid content was also higher than that of males.There was no significant difference in the composition of amino acids between the muscles of Procambarus clarkii(P>0.05).Through the rice-crayfish co-culture continuous cropping period,different paddy fields were tested by different C/N feeding modes.The results showed that the changing rules of dissolved oxygen content of all groups were consistent,showing a gradual decline trend.The dissolved oxygen content of group B was declined slightly higher than other groups whether smash strow or not,during which dissolved oxygen was in the range of 4.6 mg/L to 6.5 mg/L.The changes of pH in each group showed a trend of decreasing first and then increasing,fluctuating between 7.2 and 7.9.The total nitrogen and ammonium nitrogen in the water showed a slight increase and then increase sharply.The TP showed a consistent downward trend.The variation of nitrate nitrogen was unclear and the nitrite nitrogen content was lower than 0.01 mg/L.In summary,by increasing the C/N of feed of rice-crayfish co-culture system,the utilization rate of natural food in the rice fields can be increased.There was no significant difference of meat yield,fullness,edible rate and biochemical components also.There was significant effect on the female gonads which needs further study.There are individual differences in fatty acid and amino acid content,which may be related to the nutritional composition of feeds and natural food.Crayfish which was cultured by the means of optimizing C/N was still a nutritionally valuable aquatic product.During rice-crayfish co-culture continuous cropping period,the water quality was determined by the density and activity of Procambarus clarkii,and feeding amount of it.It was not affected by the different C/N and whether the straw was crushed.Follow-up needs to be further explored in the production of large-scale ricecrayfish co-culture systems.