The Effects Of Temperature And Photoperiod On The Behavior And Salt Tolerance Of Migratory Steelhead Trout (Oncorhynchus Mykiss)

This thesis investigates the effects of temperature and photoperiod on the growth,physiology,and behavior of steelhead trout(Oncorhynchus mykiss)in the freshwater stage under actual culture conditions and determines the optimal temperature and photoperiod combination conditions for steelhead trout in the culture environment.Four treatment groups were set up in this experiment:13℃&16L:8D(T1),16℃&16L:8D(T2),13℃&12L:12D(T3),and16℃&12L:12D(T4),and three replicates were set up for each treatment group.480 juvenile steelhead trout with an undamaged body surface were selected and randomly and equally distributed to each experimental bucket(40 fish/bucket),and the experiment was conducted for40 days in total.The main findings of the study are as follows.1.Effects of temperature and photoperiod on the growth of steelhead troutThe growth status of juvenile steelhead trout was significantly higher than the other three treatment groups under T1 conditions(P<0.05).When the photoperiod periods were the same(T1 and T2,T3 and T4),final body weight,weight specific growth rate,weight gain rate and daily weight gain were significantly higher in the low temperature treated groups T1 and T3 than in the high temperature treated groups T2 and T4(P<0.05).When the temperatures were the same(T1 and T3,T2 and T4),the final body length,final body weight,length-specific growth rate,weight-specific growth rate,length growth rate,weight gain rate and daily weight gain were significantly higher in the long photoperiod treatment groups(T1 and T2)than in the short photoperiod treatment(T3 and T4)(P<0.05).The results showed that the growth of juvenile steelhead trout in the freshwater stage was facilitated at 13°C&16L:8D,which effectively improved the growth performance of juvenile steelhead trout.2.Effects of temperature and photoperiod on the physiology of steelhead trout1)Effects of temperature and photoperiod on energy metabolism of steelhead troutAt the end of the experiment,the liver triglyceride content of steelhead trout in the T1treatment group was significantly higher than that in the T4 treatment group(P<0.05).The liver glutamate transaminase activity of steelhead trout in the T1 treatment group was significantly higher than that in the T3 and T4 treatment groups(P<0.05).The results showed that the energy supply and metabolism of steelhead trout in the 13℃&16L:8D treatment group were better compared to other treatment groups,which was beneficial to the growth and development of steelhead trout.2)Effects of temperature and photoperiod on antioxidant enzyme activities of steelhead troutAt the end of the experiment,the superoxide dismutase activity in the liver of steelhead trout in the T1 treatment group was significantly lower than that in the T4 treatment group(P<0.05),while the catalase activity and malondialdehyde content in the liver of the steelhead trout T1 treatment group were significantly lower than those of the other treatment groups(P<0.05).The results indicated that the degree of oxidative stress damage to steelhead trout was less under13℃&16L:8D compared to the other treatment groups.3)Effect of temperature and photoperiod on osmolality and cortisol of steelhead troutAdditionally,at the end of the experiment,the Na~+/K~+-ATPase activity in the gills of steelhead trout was significantly higher in the T1 treatment group than in the other treatment groups(P<0.05).Osmolarity regulation was significantly higher in the long photoperiod treatment group(T1 and T2)than in the short photoperiod treatment group(T3 and T4)under the same treatment conditions of temperature(T1 and T3,T2 and T4)(P<0.05).Furthermore,the level of brain cortisol in steelhead trout was significantly lower in the T1 treatment group than in the other treatment groups(P<0.05).The results showed that scleractinian trout had a strong osmoregulatory capacity and low stress levels under 13℃&16L:8D conditions.3.Effects of temperature and photoperiod on the behavior of steelhead trout before and after feedingRegarding the behavior of steelhead trout before and after feeding,the mean swimming speed of steelhead trout in the T1 treatment group was significantly lower than that in the T2 and T4 treatment groups(P<0.05).The maximum acceleration of steelhead trout in the T1 treatment group before and after feeding was significantly lower than that in the other treatment groups(P<0.05).Before feeding,the distance from the center of the experimental bucket and the mean distance between steelhead trout in the T1 treatment group were significantly lower than those in the T2 and T4 treatment groups(P<0.05).After feeding,the distance from the center of the steelhead trout to the experimental bucket was significantly lower in the T1 treatment group than in the other treatment groups(P<0.05).These results showed that under the conditions of13°C&16L:8D,the spontaneous activity of fish decreased,and they tended to move more towards the center of the experimental barrel.