Effects Of Different Diets On Growth And Intestinal Microflora Of Sepia Pharaonis Larvae

Sepia pharaonis commonly referred to as pharaoh cuttlefish,is one of the most easily cultured cephalopods.It is a commercially significant cuttlefish throughout the southeast coast of China and an important marine resource for world neritic fisheries.Due to its large size,rapid growth rate,short breeding cycle（up to two generations per year）,tasty meat with high nutritional value,S.pharaonis is suitable for culturing.S.pharaonis preys on live food in the natural environment.In the artificial breeding process,the use of live prey is expensive,impractical,and can be a source of pathogens or parasites.The development of S.pharaonis larvae during domesticated is an important period that determines the replenishment and breeding yield of S.pharaonis resources.This study aims to investigate changes in the GI of S.pharaonis during domestication.This paper studied the histology of the stomach,caecum,and changes in digestive enzymes of the liver.Then the intestinal flora by 16S r RNA was also be analyzed.This research provides basic information about a transition from live to dead prey affect the development of cuttlefish and developing co-feeds,which is essential for the artificial cultivation of S.pharaonis.1.After feeding with different diets for 15 days,the growth indexes of S.pharaonis were measured.The results showed that the survival rate of cuttlefish on mysid group was not significantly different from that in E.carinicauda group,but the specific growth rate and weight gain rate were significantly lower than those in chilled shrimp group（P<0.05）.After the conversion to chilled E.carinicauda feed,the carcass length and weight of cuttlefish larvae increased linearly with the culture time,and the fitting equations were y=0.6937x+1.6853（R²=0.9451）and y=2.2571e^0.4174x（R²=0.9649）.2.Results of the digestive enzyme activities in cuttlefish liver determined in the experiment were shown that the activity of amylase decreased with the development of cuttlefish larvae.The activity of lipase decreased significantly on day 7 and then increased to a plateau on day 14.The activities of trypsin decreased on day 21 and later increased,to reach the maximum level at day 28.In the initial days of mysid feeding,amylase（P<0.05）activity was significantly decreased.There was no significant difference at lipase level（P>0.05）,while,trypsin level was significantly increased（P<0.05）.The stomach morphology and thickness became increasingly developed from the first day the cuttlefish was fed on mysid to day 28 of feeding on E.carinicauda.The caecum morphology and thickness also developed from the day the cuttlefish was fed on mysid to day 28 of feeding on E.carinicauda.The D-shaped stomach of cuttlefish was surrounded by digestive glands.The stomach consists of three layers:the mucosal layer,submucosa and muscular layer.The submucosa was very thin,but the muscular layer is extremely thick.The muscular layer is mainly composed of the outer circular muscle.The luminal wall of the stomach is lined with a simple prismatic epithelium that consists of columnar cells,with a very thick cuticular layer.The caecum was short and a coiled saccus around a columella,which was connected to the intestine.The caecum also consists of three layers:the mucosal layer,submucosa and muscular layer.The muscular layer and submucosa were thin.The caecal wall bears numerous long primary leaves of the mucosa extending radially and projecting small secondary leaflets.The stomach and caecum have been fully developed,and the cuttlefish has a high plasticity to adapt to different diets.3.During the feeding period of cuttlefish,the dominant intestinal flora at the phylum level was Actinobacteria,Proteobacteria,Gemmatimonadetes,Acidobacteria and Bacteroidetes.Before and after feeding with different diets,the dominant bacteria in the intestinal flora of cuttlefish were the same,and the intestinal flora reached a relatively stable state.During the period of feeding different diets,the intestinal flora and feed flora of cuttlefish were more similar than those of water samples.In summary,the larvae of cuttlefish are highly adaptable to different feeds,which provides basic data for feeding conversion in the subsequent breeding process.