| Feeding strategies, photoperiod and dietary carbohydrate levels have a great impact on farmed fish growth and feed utilization in recirculating aquaculture. In this study, the effect of feeding frequency and feeding rates of Russian sturgeon(Acipenser gueldenstaedtii) juvenile on the growth, digestive enzyme activity and ammonia excretion was discussed. Meanwhile, the effect of photoperiod on its feeding and growth was researched, in order to explore the appropriate photoperiod of Russian sturgeon under factory conditions. And aimed at improving the utilization of high-carbohydrate diet by increasing feeding frequency, the effects of feeding frequency and dietary carbohydrate levels on the growth and glucose metabolism of Russian sturgeon was explored. Thus saving feed protein and reduce feed costs. The results can be briefly summarized as follows:1. Effect of feeding frequency on growth, digestive enzymes activities and ammonia excretion of juvenile Russian sturgeon, Acipenser gueldenstaedtiiThe growth, hepatopancreas digestive enzymes activities and ammonia excretion of juvenile Russian sturgeon, were studied at four feeding frequencies, which were2meal·d-1,3meal·d-2,4meal·d-1,6meal·d-1(F2, F3, F4, and F6), respectively for42days. The results showed that weight gain (WG) increased with the increase of feeding frequencies from F2to F6, while feed conversion rate (FCR) decreased. But no differences were found in WG among groups F6, F3, and F4. FCR of F3, F4and F6were significantly lower than that of F2. Condition factors(CF) of F2and F6were significantly lower than those of F3and F4. viscera index(VSI) and hepatopancreas somatic indices(HSI) increased as the feeding frequency increased, but significant differences among all groups were not found. Amylase and lipase activities increased with the increase of feeding frequency, while feeding frequency had no significant effects on trypsin activity. Ammonia excretion decreased with the increase of feeding frequency. Oxygen consumption rate of F6was significantly lower than that of other groups. The results suggest that, appropriately increase of feeding frequency could improve the digestive enzyme activities, nutrient digestibility, and reduce the proportion of protein metabolized as energy, in order to improve the growth and feed utilization of juvenile Russian sturgeon. Combined the results of this study and the practice of Russian sturgeon production, feeding frequencies equal to or more than4meal·d-1are recommended to farm Russian sturgeon juveniles.2. Effect of photoperiod and feeding rate on growth and digestive enzymes activities of juvenile Russian sturgeon, Acipenser gueldenstaedtiiThe growth and digestive enzymes activities of juvenile Russian sturgeon, were studied at two photoperiods (natural photoperiod and all dark) and three feeding rate (satiation,85%satiation and70%satiation). The results showed that compared with natural photoperid, there were lower FCR, VSI, HSI, trypsin activity and amylase activity in the all dark. In the case of only feeding rates be considered, WG, FCR and HIS decreased as the feeding rate decreased. While the intestinal trypsin activity of juvenile Russian sturgeon increased with the feeding rate decreased. CF of85%satiation was the highest and significantly higher than those of satiation. In addition, the CF, VSI, crude protein(CP), lipase activity and amylase activity of70%satiation were lower than the other two feeding rate groups, but the moisture of it was the highest. While the VSI, CP, lipase activity and amylase activity of satiation and85%satiation were no significant difference. There were interaction of two experimental factors at VSI, ether extract (EE) and trypsin activity, suggested that all dark promoted the increase of VSI and EE of fish feed to satiation. In summary, the feeding rates of juvenile Russian sturgeon can be slightly reduced will not have a significant impact on their growth, but lower than85%was inadvisable.In addition, all dark is no significant effect on the growth of juvenile Russian sturgeon, but can promote the storage of energy at higher feeding rates.3. Effect of feeding frequency and carbohydrate levels on growth, hepatic glucose metabolism enzymes and blood physiological and biochemical of juvenile Russian sturgeon, Acipenser gueldenstaedtiiThe growth, hepatic glucose metabolism enzymes and blood physiological and biochemical indexes of juvenile Russian sturgeon, Acipenser gueldenstaedtii, were studied at two feeding frequencies (2meal·d-1and6meal·d-1) and four carbohydrate levels (14%、21%、28%'35%), respectively for56days. The results showed that the juvenile Russian sturgeon fed at higher feeding frequency had higher survival, WG, CP, EE and lower moisture. The triglycerides(TG) and blood glucose of serum and the activity of three hepatic glycometabolism enzymes were higher in the higher feeding frequency groups, while the activity of Lysozyme、Alanine aminotransferase(ALT) and Aspartate aminotransferase(AST) were opposite to the above. However, increased the feed starch content, the WG, CP and ash were decreased while the moisture was increased, and the survival was also significantly decreased when the feed starch content to35%. When the feed starch content increased to28%, the EE was significantly increased. The activity of hepatic glycometabolism enzymes were decreased with increased of the feed starch content. There were interaction of two experimental factors only at the survival, GH, EE and TG, suggested that, higher feeding frequency can improve survival of juveniles fed a high starch diet, and only at the higher feeding frequency can the high starch diet be fully utilized. In summary, the juvenile Russian sturgeon should be fed at a high feeding frequency (e.g.6meal·d-1), and the carbohydrate content of the feed can be appropriately increased to28%. |
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