| Based on red tilapia as the research object, the experiment is divided into two parts:(1)through the acute salinity (0,5,10,15,20,25,30) and salinity domestication experiment (Ingradually increasing water salinity with1,2,3,4,5once a day) to explore the salinity tolerance ofred tilapia.(2) set0,5,10,15and20salinities, raising health red tilapia50d which the originalweight and length were8.75±0.04g,8.79±0.54cm, respectively. To study the influences ofsalinity on growth, digestive enzyme activities, muscle composition, hematological andbiochemical indices, and the activities of ATPase of red tilapia.1. Salinity tolerance of Red TilapiaThrough the acute salinity(directly transferred from freshwater to brackish waters withdifferent salinity5,10,15,20,25,30) and salinity acclimation experiments(gradually increasingwater salinity1,2,3,4,5once a day) to study the salt tolerance of red tilapia.The results showedthat the salinity of death interval was15~20. The LC50were17.72,17.00and16.73g/L in theconditions of48,72and96h and its reduced with the prolonged of salinity experiment. Therewas a significant correlation between the logarithmic of salinity and mortality(P<0.05), and thesalinity of safety is1.673g/L. When domesticated gradually salinity rising, the salt resistancecould adapt to26.2. Effects of Salinity on Growth, Digestive Enzyme Activities and the ratio of RNA/DNA of RedTilapiaThe red tilapia were raised under the condition of different salinities (0,5,10,15and20)50d, which be acclimation by the salinity. The results showed as follows:(1) the survival ratesand the fat factors were no significant difference (P>0.05); the feed factors were increased by thesalinity increasing, except for the0and5salinity experiment, there were significant difference(P<0.05)；the growth rates and the specific growth rates were significant difference (P<0.05).(2)In the condition of different salinities (0,5,10,15and20),the activities of protease,amylaseand lipase in hepatopancreas were significant difference (P<0.05) as the same to the intestineand stomach. The activities of digestive enzymes were significant difference among thedifferent digestive organs (P<0.05) and the order of protease, amylase and lipase activities were intestine＞stomach＞hepatopancreas, intestine＞hepatopancreas＞stomach, hepatopancreas＞intestine＞stomach, respectively.(3) The ratio of RNA/DNA were increased with the salinityincrease and there were significant difference between them (P<0.05) except for15between10and20. These results indicate that the effects of salinity on the growth, activities of digestiveenzymes and the ratio of RNA/DNA in red Tilapia were significantly inhibited，which directlyaffect their growth and development.3. Effects of salinity stress on the antioxidant enzyme activities in Red Tilapia blood and theATPase activities in its gillUnder the condition of different salinities (0,5,10,15and20), the activities of Superoxide dismutase (SOD), Catalase (CAT), peroxidase (POD), glutathione peroxidase (GSH-PX)，glutathione S-transferase (GST) and glutathione reductase (GR) in the blood of red Tilapia weresignificant difference (P<0.05), respectively. The activities of Na+/K+-ATP had a trend ofdecreasing after an initial increase, and reached the highest value at5salinities, there weresignificant difference (P<0.05) expect that of15salinities and20salinities. The activities ofCa2+/Mg2+-ATP had a trend of decreasing after an initial increase, and reached the highest valueat10salinities. there were significant (P<0.05) expect that of5salinities and20salinities. Theresults indicated that the increase of water salinity could significantly improve the antioxidantenzyme activity and ATP enzyme activity, however, the ATP enzyme activity has been restrictedunder the condition of high salinity.4. Effect of Salinity stress on muscle quality of Red TilapiaUnder the condition of different salinities (0,5,10,15and20) were studied, the resultsshowed as follows: the moisture were increased by the salinity increasing, except for the0salinity experiment, there were no significant difference (P>0.05); the crude protein weredecreased by the salinity increasing, there were significant difference between them(P<0.05)except for the0and5salinity experiment; the crude fat were decreased by the salinity increasing,except for the5and10salinity experiment, there were significant difference betweenthem(P<0.05); the crude ash were no significant difference (P>0.05) except for the20salinityexperiment has a significant decreased, The content of glutamic acid were16.13±0.02%,16.32±0.02%,16.26±0.01%,16.10±0.02%and16.11±0.02%in muscle of red tilapia,respectively, which was the highest among the17amino acids, the lowest was cystine, whosecontent were0.62±0.01%,0.58±0.02%,0.53±0.01%,0.52±0.01%and0.52±0.03%, respectively.The content of essential amino acids were40.8±0.01%,40.9±0.03%,41.2±0.03%,41.3±0.02%and41.0±0.04%, respectively. The ratio of essential amino acids/non-essential amino acid were 81.4±0.01%,81.4±0.01%,82.7±0.09%,83.2±0.09%and, respectively. The content of deliciousamino acids were38.2±0.02%,38.5±0.02%,40.3±0.01%,41.1±0.02%and41.7±0.02%(P<0.05), respectively. Therefore, feeding in brackish water can enhance the flesh quality of thered tilapia, and the delicious of the fish was increased by the salinity increasing. |
