| 1,Tissue-specific changes of NKCC1a mRNA under gradual stress of salinity in"GILI"tilapiaQuantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) was used to study the tissue-specific changes of NKCC1a expression by salinity in case of the hybrid (named"GILI"tilapia) by O.niloticus(♀)×S.melanotheron(♂). Being a new variety,"GILI"tilapia is characterized by high salt tolerance and fast growth both and is suitable for marine culture. The present results showed that: (1) The NKCC1a mRNA expression level has a significant tissue specialty: the NKCC1a gene expressed in all the tested tissues of gill, liver, kidney and intestine when salinity below 25. When the salinity increased from 0 to 48, the NKCC1a mRNA expression level showed a positive correlation in gill (R>0.9, P<0.01), but negative correlation in intestine and kidney (R≈-0.7, P<0.05) and no correlation in liver. (1)When the salinity raised to 64, the mRNA expression level reached the highest peak after 3h in gill and intestine, and decreased after 5h, and there were significant differences from 1h to 3h and 3h to 5h (P<0.05). In liver, the maximum level appealed in 5h and significantly higher than those in 1h and 3h(P<0.05). In kidney, the levels descended continually with the increase of time, but no statisticaly significant differences were detected among them. (2)Above results revealed that, in the"GILI"fish which acclimates to environmental salinity over 25, it is primarily the gill chloride cell to secrete the cation ions and to maintain water and salt balance. So, it is considered that gill plays a leading role in hyper-osmoregulatory of"GILI"tilapia. Meanwhile, we are expected to provide a guidline for revealing the expression mode of NKCC1a gene in euryhaline teleosts in fresh, saline and hypersaline water.2,The expression changes of NKCC1a mRNA under sharp stress of salinity in"GILI"tilapiaThe stress response of"GILI"tilapia, juveniles[body mass(21.4±5.4)g],following abrupt transfer to salinities 20 and 25 were studied. The present results showed that: (1) the mortality was only 12% at salinity 20 during the first 24h, and almost unchanged after that; a mortality of 100% was observed at salinity 25 within 5.35h. (2) At salinity 20, The NKCC1a mRNA expression in the gill increased rapidly, and reached the peak at 6h, being 17.49-fold of the control, then gradually decreased; and the level of 12h and 24h were significantly higher than the fresh water (P<0.05); The expression of the intestine and kidney appeared to have the initial level after a decline trend. In the intestine, it decreased to the minimum at 8h, being 28.4% of the freshwater, but there were no significant difference among 12h,24h and freshwater(P>0.05); In the kidney, the level of 6h was 20.86% of the control, and there were no significant difference between 24h and freshwater. (3) At salinity 25, The mRNA expression of the gill content a decline trend after a rise of 4hs, the level of 4h were 4.31 times higher than the control, and there were significant difference between 4h and 5h (P<0.05); in the kidney, there were no significant changes during the 5hs; the expression of the intestine were similarly with that at 20 ppt, and decreased significantly (P<0.05). Collectively, above results indicated that:"GILI"tilapia could not directly adaption to salinity 25 may be related to the limit capacity of gill and kidney to up/down-regulate NKCC1a expression, and gill and kidney plays a leading role in the process of secrete the monovalent ions after abrupt salinity transfer.3,Cold tolerance of GILI Tilapia, NEW GIFT Nile tilapia and Black-chin tilapiaCold tolerances of three tilapias(NEW GIFT Nile tilapia,GILI Tilapia and Black-chin tilapia)to low temperatures naturally decreased in the Shanghai area were studied and the average lethal temperature of 50% individuals were calculated continuously for 3 years. It is found that Low lethal water temperatures ranged from 7.5℃to 5.8℃,and the average lethal temperatures of 50% individuals was 6.8℃for NEW GIFT Nile tilapia in 2008. Meanwhile, behaviors of tilapias under decreasing water temperatures were observed. The range of Low lethal water temperatures were 10.8～7.6℃,12.4～9.2℃for NEW GIFT Nile tilapia and GILI Tilapia in 2009, and the average lethal temperatures of 50% individuals were 9.2℃and 11.4℃. But they were 10.8～7.6℃,12.4～9.2℃and 13.8～12.4℃for NEW GIFT Nile tilapia,GILI Tilapia and Black-chin tilapia in 2010. The average lethal temperatures of 50% individuals were 8.3℃, 12.5℃and13.1℃, separately , also there were significant differences among them. The comprehensive results showed that:water temperatures that beginning die and100% die were 11℃,5.8℃respectively for NEW GIFT Nile tilapia, 12.4℃,9.2℃respectively for GILI Tilapia,13.8℃,12.4℃respectively for Black-chin tilapia. There were significant or highly significant species/strain-specific differences among these three genotypic tilapias in cold tolerance. The hybridization could improve cold tolerance to a certain extent. |
