| 240tails of Israeli red tilapia (Oreochromis sp.) were randomly divided into4groupstriplicate. They were all tanked at23℃for a week, then culture at23℃,20℃,17℃and14℃for9days respectively, with a cooling regime of1.5℃/d. The fishof each group weresampled before and after the experiment. The feed intake (FI), survive, biological parameter,composition of the muscle and hepatopancreas, metabolites of the serum, fatty acidscomposition of the hepatopancreas, the antioxidant index and3kinds of vitamins weredetermined. The main results are listed below:The fish could not endure the long term stress at14℃, for they almost stopped eating at thistemperature. After the experiment, erosion of the fins and hyperaemia of the base of thepectoral fins and one fish died at14℃. The FI and body surface of other groups were normal.After the experiment, the hepatopancreas index (HI) of17°C group was significantly higherthan others (P<0.05), followed by20°C group, this may the adaptation to the lowtemperatures.The low temperature would influence the compositon of muscle and hepatopancreas. After theexperiment, the moisture of hepatopancreas of14°C group significantly increased3.5percent(P<0.05), this might caused by the decrease of the lipid and hepatic glycogen. After theexperiment, the crude lipid of17°C group significantly (P<0.05) higher than other groups,this may the adaptation to the low temperatures.Before the experiment, the GLU of the14°C group reached highest to6.67mmol/L; after theexperiment, it dropped extremely to3.7mmol/L (P<0.01), but still significantly higher thanothers (P<0.05). Before the experiment, the total triglyceride (T-TG) of the serum increasedwith the temperature, got its maxima at17℃group to3.37mmol/L; after the experiment,17℃group was still highest at6.96mmol/L, and the14℃group dropped obviously72.5percent (P<0.05), to0.75mmol/L. The total cholesterol (TC) of the serum dropped with thetemperature, before the experiment, the differences between groups were not significant(P>0.05); after the experiment,14℃group was the lowest, dropped significantly23.02percent to4.19mmol/L (P<0.05). Only at14℃group, the total protein (TP) of the serumdropped dramatic23.8percent to23.42g/L after the experiment (P<0.05). The drop of the TPmight affect the T-TG and TC in the serum. The low temperature stress would influence themetabolites in the serum considerably. At17℃group，the T-TG was always the highest and this might be adaptation phenomenon. At14℃group, the decreasing of GLU, T-TG, TC andTP was obvious (P<0.05) and this showed serous stress.At low temperature hepatopancreas performed adaptation change, at14℃group theUFA/SFA increased4.6percent (P=0.24) after the experiment, but the DHA dropped15.7percent (P=0.14). Compared with the cold adaptation of fatty acids of other fish, theadaptation level, speed and way of the experiment fish might not allow it to sustain the lowtemperature stress.Before the experiment, the total superoxide dismutase (T-SOD) of the serum were notdifferent significantly between groups (P>0.05); after the experiment,17℃group obviouslyincreased30.5percent to68.83U/mL (P<0.05),14℃group was the lowest at39.24U/mL.Before the experiment, the malondialdehyde (MDA) of the serum were not differentsignificantly between groups (P>0.05); after the experiment, MDA of the serum dropped withthe temperature,14℃group dropped dramatic33.34percent to6.1nmol/L (P<0.05). In lowtemperature, the peroxide stress in the fish did not increase within the experiment and thismight because the form of reactive oxygen species (ROS) in the fish body decreased with thetemperature.Before the experiment, the ascorbic acid (VC) of the plasma were not different significantlybetween groups (P>0.05); after the experiment, the control group was20.51μg/mL andsignificantly higher than other groups (P<0.05),14℃was the lowest at16.17μg/mL. The VCcontents of the hepatopancreas at14℃group dropped obviously (P<0.05), before theexperiment was26.5percent lower than the control, to555.19μg/g; after the experiment was62.5%percent lower than the control, to266.6μg/g. The retinol (VA) and α-tocopherol (VE)in the plasma was always highest at17℃group.After the experiment at the14℃group, VAdropped obviously69.5percent to0.037μg/mL (P<0.05); VE dropped obviously25.7percentto11.89μg/mL (P<0.05). At14℃group, the VA and VE in the plasma all decreasesignificantly (P<0.05) after the experiment, so did the VC in the hepatopancreas, these mightcause deficient syndrome of vitamins in the fish, and this might also connect with the fact thatthe fish could not endure the stress at14℃. The VC in the hepatopancreas decreased fasterthan in the plasma and the hepatopancreas might be the main store place of VC.The fat soluble vitamins in the plasma were connected with the triglyceride (TG) in the serum.At17℃group, when thetotal triglyceride (T-TG) of the serum increased, VA and VE werealso increasing; at14℃group, when the T-TG of the serum decreased, VA and VE were alsodecreasing. The fat soluble vitamins decreased with the T-TG, this might caused by thedropping of the proteins which transported them. The two kinds of vitamins might also storemainly in the hepatopancreas. This paper also discussed how to study the effect of temperature on fish and the overwinteringproblem of fish. |
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