Reducing Crowding Interaction Improves Survival,Behavior,Growth and Disease Resistance of Juvenile Sea Urchin Strongylocentrotus intermedius
Juvenile sea urchin Strongylocentrotus intermedius with test diameter of about 1.0 cm were reared in a tank with a length of 19.6 cm×a width of 16.8 cm×a height of 18.5 cm at stocking density of 24 individuals per tank,with different crowding in contact with each other:in the highly crowded group H,all of the sea urchin was directly placed in the tank;in the medium-crowded group M the tank was divided into upper,middle and lower layers with horizontal partition,in which 8 juveniles were placed in each layer;and in the low-crowded L group the tank with upper,middle and lower layers by a horizontal partition as in the group M was again divided into 24 small compartments by vertical partition of 2×4 per layer of longitudinal compartments,one sea urchin per compartment at normal water temperature,and same feeding management for 5 weeks.At the end of the experiment,the body size,lantern growth,gut weight and histological morphology,and tube foot extension of the sea urchins were measured and observed in each group.One week later,10 healthy sea urchin in each group were randomly placed in a tank with three sea urchin died of blackmouth disease for five days to observe and calculate the morbidity and mortality rate of the sea urchins in each group,aiming to evaluate the effects of reducing crowding on the behavior,growth and disease resistance of the sea urchin juveniles.It was found that the sea urchin in group L had significantly larger test diameter of(17.18±1.51)cm and body weight of(2.57±0.59)g than those in group H which test diameter was(15.53±1.68)cm and body weight was(2.01±0.56)g did(P<0.01).There was significantly higher gut weight in the sea urchin in the group L(0.14±0.07)g than those in the group H(0.07±0.03)g,with intestinal ring folds arranged neatly,and the normal cell morphology,almost without tissue cavitation.This can be explained by the greater food digestion and faster growth rate in the sea urchin in low interactions.This morbidity was significantly reduced in sea urchin in group L(21.25±13.56)%than those in group H(67.14±14.96)%.The finding indicated that reducing the interactions each other led to greatly improve the growth and disease prevention efficiency of sea urchin during juvenile rearing period,suggesting a new technique(high stocking density and low interactions)for the intermediate culture of sea urchin.
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