Changes In Morphology, Histological Structure, And Biochemical Components During Overwintering In Cyprinus Carpio Var. Songpu Mirror

Common carp(Cyprinus carpio) is major fish species cultured in ponds in high latitudes northern China with long and cold winter. The common carp reaches market size after experiencing a five months overwintering period in Northeast China. Thus, it is critical to understand the effects of overwintering on survival and growth of the cultured fish.In this study,the growth of Songpu mirror carp was monitored using passive integrated transponders before and after overwintering. All fish were hatched at the same time and cultured under the same conditions. Morphological indices, liver and foregut histological structure, and biochemical components of the viscera, muscle and the whole body were analyzed at 125d(before overwintering), 170d(freezing beginning) and 325d(after overwintering). Furthermore,the correlation between major energetic materials at 325 d and overwintering body weight loss rate(WRL) was evaluated. The results were summarized as follows:(1) The results showed that body weight(BW), condition factor(CF), visceral-somatic index(VSI), hepatosomatic index(HSI), and intestine-somatic index(ISI) decreased significantly over the entire overwintering period(125~325 d)(P<0.05). The weight of the carp body change is significantly obivious. Body weight were signifacantly decreased in every period overwintering(P<0.05); Liver and bowel weight is decreased significantly in the phase of overwinter(170d~325d); Length parameters(body length and bowel length) is no significant difference in the detection time(P>0.05). Condition factor(CF), visceralsomatic index(VSI), hepatosomatic index(HSI) and intestinosomatic index(ISI) were significantly decreased in the whole overwintering period(125d~325d)(P<0.05).The VSI determination were significantly decreased in the whole overwintering period(P<0.05), decreased by 21.47%,18.96%.And CF were significantly decreased in the phase of freezing(125d~170d). The change of HSI and ISI showed the same trend as liver weight and bowel weight.(2) Significant degeneration of histological structures for the hepatic and foregut was observed during 125~325 d. Hepatic cells shrank, and the boundaries between hepatic cells were blurred. The abundant hepatic glycogen and lipid stores present before winter disappeared after winter. Foregut diameter, villus height, and muscle layer thickness decreased significantly after winter compared with those before winter(P<0.05), and the striated borders of the foregut were clearly atrophied.(3) Visceral fat and hepatic glycogen contents were significantly attenuated at each sampling period(P<0.05). However, whole-body and muscle protein contents only decreasedsignificantly during 170~325 d(P<0.05). In addition, a significant negative correlation was detected between muscle protein content at 325 d and WRL(P<0.05), but no association was found between visceral fat at 325 d and WRL.Taken together, these results suggest that overwintering led to significant changes in the morphological indices based on common carp BW. Degeneration of the hepatic and foregut histological structures resulted from chronic hunger during the winter. The stages of consuming endogenous energy during the winter varied. Hepatic glycogen and fat were used initially during125~170 d, whereas hepatic glycogen, fat, and protein were used for energy during 170~325 d.Muscle protein content after the winter could be useful as a WRL reference indicator.