Effects Of Salinity-alkalinity On Growth, Osmophysiology And Relative Expression Of Gill Ion Transport Enzymes Of Oreochromis Niloticus

To understand acute salinity tolerance and growth performance of Nile tilapia insalinity-alkalinity water aquaculture and the physiological change processes inadaption to salinity and alkalinity water, and this study used three strains of Nile tilapiaOreochromis niloticus juvenile and adult fishes as experimental material, and the acutechange of serum osmolality, serum Na+, K+, Cl-concentration and mRNA expressionof Na+-K+-ATPase (NKA) and carbonic anhydrase (CA) in gill of different treatmentgroups were observed in96h, Results were as follows:(1) The survival rate and average growth rate of Nile tilapia juvenile fishes ofShanghai, Shandong and Hebei strains, chronically acclimated before experiment, areevaluated in net cage under different salinity water (S0、S15、S20), NaHCO3alkalinitywater (A1g·L-1、A2g·L-1、A3g·L-1), and salinity-alkalinity water (SA15,1、SA15,2、SA15,3、SA20,1、SA20,2、SA20,3). The62-days experiment result shows there is nosignificant difference in the survival rate among three strains under different salinities,alkalinities and saline-alkali waters (P>0.05), while significant difference in averagegrowth rate exist (P<0.05). The average growth rate of three strains tend to roughlydecline with increasing salinity and alkalinity treatments, the salinity-alkalinitytreatments show slower growth rate compared with the salinity treatments and alkalinity treatments. Shanghai, Shandong and Hebei strain also show some relativegrowth advantage in different salinity and alkalinity gradients, respectively. Theseresults provide some basic data for optimum growth salinity-alkalinity determination,strain selection of Nile tilapia.(2) In order to assess the tolerance and growth performance of Nile tilapia insalinity-alkalinity waters, salinity-alkalinity tolerance of Shanghai, Shandong andHebei strains, which were acclimated and cultured in salinity-alkalinity water atjuvenile stage, were measured and the average growth rate at differentsalinity-alkalinity waters (S0A0, S10A0, S10A2, S10A4, S10A6) were comparedduring60days culture experiment. The results showed that the96h median lethalsalinity of young fish of Shanghai, Shandong, Hebei strain was18.528g.L-1,20.347g.L-1,19.342g.L-1, respectively, whereas the96h median lethal NaHCO3alkalinity was8.827g.L-1,8.540g.L-1,8.542g.L-1. For mixed salinity-alkalinity tolerance,96h lethalalkalinity at10salinity was Hebei strain (4.377g.L-1)> Shanghai strain (3.561g.L-1)>Shandong strain (3.108g.L-1), at15salinity, it was2.144g.L-1,2.183g.L-1,2.183g.L-1for Hebei, Shandong and Shanghai strain, respectively (P>0.05). The alkalinitytolerance of Nile tilapia at high salinity was significantly lower than that at the lowsalinity (P<0.05). The growth experiment result showed that there was no significantdifference among average growth rate of adult fish in S0A0, S10A0and S10A2,however, the growth rate decreased at S10A4and significantly at S10A6(P<0.05).Hebei strain showed a relatively high growth rate than Shanghai, Shandong strains inS10A2, S10A4and S10A6(P<0.05). These results provided the basic data for thesuitable culture salinity-alkalinity waters and selection breeding for Nile tilapia.(3) To understand the physiological change processes in adaption to salinity andalkalinity water, Nile tilapia were divided into four groups and directly transferred intofour salinity-alkalinity treatments (A: salinity10,1g.L-1NaHCO3; B: salinity10,2g.L-1NaHCO3; C: salinity15,1g.L-1NaHCO3; D: salinity15,2g.L-1NaHCO3) fromfreshwater, the acute change of serum osmolality, serum Na+, K+, Cl-concentration and mRNA expression of Na+-K+-ATPase (NKA) and carbonic anhydrase (CA) in gill ofdifferent treatment groups were observed at0,6,12,24,36,48,72and96h,respectively. Results showed that the change of serum osmolality, serum Na+, K+, Cl-concentration, and NKA, CA mRNA expression was relevant to the salinity-alkalinitystress levels. Meantime, these parameters share a similar up-peak-down change trend.The serum osmolality in B, D treatments reached the peak at24h, while A, Ctreatments at36h. Serum Na+, K+, Cl-concentration in all treatments reached the peakat24h. The highest NKA mRNA expression in B, D treatments was detected at36h,while24h in A and C treatments. The highest CA mRNA expression in B, C and Dtreatments was observed at24h. These results showed O. niloticus could adapt tosalinity-alkalinity water to certain degree, NKA and CA were involved in iontransportations and osmolality balance under salinity-alkalinity stress.