| Tilapia is native to Africa. Tilapia is a euryhaline fish. Now tilapia isa every famous kind of fish because of its resistance to coarse grains,hypoxia and disease. Here, this thesis focused on growth comparisonamong different families of Oreochromis niloticus♀×Sarotherodonmelanotheron♂F2, different genetic types of tilapias under differentsalinities, providing some data for breeding of salinity-tolerance tilapia.Meantime, salinity effect on mTOR pathway factors was also investigated,which would provide a new direction to understand the mechanism ofsalinity effect on growth in tilapia.1. Comparison on salt tolerance and growth between familyoffsprings and mixed group of Oreochromis niloticus♀×Sarotherodon melanotheron♂F2F2family offsprings and mixed group were obtained by paired andmixed mating the hybrid F1individuals of Oreochromis niloticus♀×Sarotherodon melanotheron♂, respectively. The salt tolerance andgrowth under different salinities (0g/L,15g/L,20g/L,25g/L) of juvenile fishes from two mating modes were compared. The results showed thatMST, ST50, MLS-96of O. niloticus♀×S. melanotheron♂F2were higherthan that of the control group O. niloticus (P＜0.05). No significantdifferences in MST, ST50and MLS-96indexes were observed betweenthe family offsprings and mixed group (P＞0.05) except for the family2.Under the same salinity conditions, there wasn’t significant difffernces inthe average growth rate between the family offsprings and mixed group(P＞0.05) with a exception of family5in0g/L sanility, O. niloticus♀×S.melanotheron♂F2exhibited the lowest weight coefficient of variation at25g/L sanility. The results provided some basic data for hybrization andand utilization of O. niloticus×S. melanotheron.2. Growth comparison among three different genetic types of tilapiasunder different salinitiesThe fry salinity tolerance and growth rate at young and adult fishstages among three genetically different tilapias (Oreochromis niloticus,O. niloticus♀×Sarotherodon melanotheron♂F2and O. niloticus♀×(O.niloticus♀×S. melanotheron♂F1)♂were compared in this study. Theacute salinity tolerance result showed that mean survival time (MST50),median survival time (ST50) and median lethal salinity-96h (MLS-96) ofO. niloticus♀×S. melanotheron♂F2were significantly higher than that ofO. niloticus and backcrossing BC1(P＜0.05), MST, ST50and MLS-96ofbackcrossing BC1was higher than that of O. niloticus. Chronic salinity tolerance showed that MLS-X of O. niloticus♀×S. melanotheron♂F2,backcrossing BC1and O. niloticus was73±5.66,71.67±4.5,58.33±3.68,respectively. Backcrossing BC1was significantly higher than O. niloticus(P＜0.05), but lower than O. niloticus♀×S. melanotheron♂F2(P＞0.05). In the young fish stage, daily body weight gain of O. niloticus wassignificantly higher than that of O. niloticus♀×S. melanotheron♂F2andbackcrossing BC1under0g/l and15g/L salinities (P＜0.05). In salinityof20g/L and25g/L, daily body weight gain of O. niloticus♀×S.melanotheron♂F2was higher than that of O. niloticus and backcrossingBC1(P＜0.05). In the stage of adult fish, daily body weight gain of O.niloticus under0g/l was higher than that of backcrossing BC1and O.niloticus♀×S. melanotheron♂F2. However, in salinity of15g/l,20g/l and25g/L, daily body weight gain of O. niloticus♀×S. melanotheron♂F2wasgreater than that of backcrossing BC1and O. niloticus. These resultswould provide some basic data for hybridization breeding of salinitytolerated tilapia.3. Effects of salinity on growth of Oreochromis niloticus throughmTOR signal pathwaymTOR signal pathway plays a vital role in the regulation of animalgrowth and development. In this study, growth rate of Oreochromisniloticus under different salinities were compared in a30-day experiment;in the meantime, expression change of downstream pathway regulation factors p70s6k and4ebp1were evaluated at both mRNA and proteinlevels. The results showed that salinity significantly inhibited the growthof Nile tilapia, the final body weight decreased with the salinity increase,average body weights at0g/L,15g/L,20g/l,25g/L salinities were0.48±0.13g/d,0.31±0.09g/d,0.14±0.08g/d,0.09±0.03g/d, respectively.The p70s6k mRNA expression level decreased with salinity increasing,the highest was detected in0g/l salinity, while the lowest was in25g/lsalinity, which was significantly lower than that in0g/L,15g/L and20g/Lsalinities. The4ebp1mRNA expression at25g/L salinity wassignificantly higher than0g/l,15g/L,20g/L, increasing with salinitylevels. Western blot results showed the protein level of p70s6k at0g/Lsalinity was significantly higher than that at other higher salinities, while4ebp1at25g/L salinity was significantly higher than that at other lowersalinities. Our result suggested salinity may affect growth of O. niloticusthough mTOR signaling pathway. |
PDF Full Text Request