Behaviour of rainbow trout(Oncorhynchus mykiss) under defensible and indefensible patterns of food delivery

The goal of this study was to investigate the behaviour of rainbow trout(n=30),Oncorhynchus mykiss,in small raceways when either self-feeders(T2) or hand-feeding(t2) were used.The method of food delivery in T2 was defensible while that of t2 was indefensible.Fish in both raceways were subjected to restricted feeding(RF) for 25 days.Food was available in the morning(09:00-10:00) in the downstream area and in the afternoon(16:00-17:00) in the upstream area of the raceways.The results showed that the behaviour of rainbow trout was significantly different under interference competition(T2) for food compared with that under scramble competition(t2).RF in T2 fish limited food availability to meal times when feeding rewards were available while t2 fish only responded to the location of food delivery.The aggressive fish in T2 were dominant,and t2 fish at high densities showed intense social interactions under the indefensible pattern of food distribution;these interactions did not dampen to a minimum level to suppress the development of dominance hierarchies.Further,the stocking density did not break down the dominance hierarchies between the T2 fish.This suggests that decreased efficiency in the search for food or inefficient foraging,induced by interference competition at high densities,affected the behaviour of rainbow trout.

Clinical feature and predictive factor analysis for spontaneous regression of retinopathy of prematurity in a Chinese population

AIM:To investigate the ratio of spontaneous regression of retinopathy of prematurity(ROP)and to explore the possible relevant predictive factors.METHODS:A retrospective review of 405 infants who were diagnosed with ROP and mother during pregnancy were collected.Stage,zone,and duration of ROP were recorded.Statistical analysis was performed on 51 possible predictive factors.RESULTS:Totally 356 infants showed spontaneous regression.The incidence was 100%,95.3%,and 22.7%in stage 1,2,and 3,respectively.The 13.4%of the ROP with plus disease eventually resolved spontaneously.All affected eyes of aggressive posterior retinopathy of prematurity(APROP)failed to spontaneously regress.The mean duration of ROP was 7.2wk in patients with spontaneous resolution of ROP.Days of mechanical ventilation(OR=0.981,95%CI,0.965-0.997,P=0.021),retinal hemorrhage(OR=0.173,95%CI,0.064-0.470,P=0.001),delivery pattern(OR=2.750,95%CI,1.132-6.681,P=0.025),maternal anemia in pregnancy(OR=0.142,95%CI,0.036-0.563,P=0.005),the stages(at initial diagnosis OR=0.183,95%CI,0.041-0.816,P=0.026;at final diagnosis OR=0.031,95%CI,0.006-0.167,P<0.001),and with plus disease or not(OR=0.005,95%CI,0.001-0.031,P<0.001)were independent predictive factors of the spontaneous regression of ROP.CONCLUSION:Most mild ROP can spontaneously resolve.Active treatment is still recommended for stage 3 ROP,zone I ROP,AP-ROP,and ROP with plus disease.Prolonged mechanical ventilation and concurrent retinal hemorrhage reduce the likelihood of spontaneous ROP resolution.The pattern of delivery and the mother's anemia during pregnancy can also affect the prognosis of ROP.