Abstract:

In order to know the effects of salinity chronic stress on feeding, growth and biochemical composition of juvenile mullet (Mugil cephalus), the tame mullet juveniles (Mugil cephalus) were cultured at water salinity 20, 15, 10, 5 and 0 for 20 d, respectively, with feeding rate, special growth rate (SGR) in body weight and body length, RNA/DNA value and the biochemical composition of muscle determined on the 0th d, 5th d, 10th d, 15th d and 20th d. To facilitate the presentation, S20 was used to stand for the experiment group with the salinity 20, the same as S15, S10, S5, S0. The results revealed that the feeding rates were highly salinitydependent (P < 005) at the beginning of the experiment. Low salinity had an obvious inhibitory effect on the feeding rates of juvenile mullets. Compared with the beginning, the feeding rates had a great advance at the end of the experiment (20th d). The feeding rates of juvenile mullets in S0, S5 were increased from 567%, 579% to 1290%, 1299%. The SGR in body weight and body length were also sensitive to the changes of salinity of water. At the beginning of this experiment, the SGR in body weight and body length were quite different among different salinity groups. The SGR in higher groups such as S20, S15 were higher than in lower groups (S5, S0) (P<005). The SGR of juvenile mullets under the same salinity increased as the experiment went on. The gap between various salinity groups also gradually became narrow. At the end of the experiment, the SGR in lower salinity groups became very close to the higher salinity groups (P>005). The test results of RNA/DNA value also revealed that at first the juvenile mullets grew better when they lived in high salinity water, and then the gap became smaller among these experimental groups, which were consistent with the above rules. The biochemical composition of juvenile mullets was significantly affected by low salinity stress (P <005). The testing results of juvenile mullets muscle showed that the mullets body had a highly content of moisture which accounted for about 75% of the body weight. And the fat and protein contents were occupied about 9% and 6%, respectively. The ash content was the lowest in mullets muscle. The content of moisture in muscle increased with decreased salinity (P<005). At first, the water content in mullets muscle in lower salinity environment was higher than in higher salinity environment, with a ratio of 73% in S0 while 70% in S20. The ratios of moisture became bigger with the experiment, and the ratio in S0 even reached 78% at the end of the experiment. Though the salinity, too, had noticeable impact on the ratios of fat, protein and ash in mullets muscle (P<0.05), the change regulation of fat, protein and ash were quite different with the variation of moisture. The ratios that fat, protein and ash occupied in body weight of juvenile mullets increased with the decreased salinity and the increased test time.