Effects of NaCl and NaHCO3 on growth and gill microstructure in ju-venile <I>Barbus capito</I>

Abstract

We evaluated the effects of salinity and alkalinity on growth,feeding,and gill microstructure in juvenile Barbus capito.The fish were reared at salinity of 0(control group),2.0,4.0,6.1,7.8,10.0,or 11.9 for 60 d with temperature of 22-25℃.The body length,body weight,and specific growth rate(SGR) of juveniles were signifi-cantly lower in fish held at salinities 6.1 than in those held in salinity 6.1(P0.05).The maximum final body weight was highest in the fish reared at 2.0.The specific growth rate of weight(SGRW) and feed conversion effi-ciency(FCE) were highest in fish held at 4.0 and lowest in fish held at 11.9.Our results suggest the optimal salin-ity for growth is 1.88,whereas exposure to levels ≥7.8 results in negative effects.Fish were also reared at 10.00,15.83,25.10,39.80,and 63.12 mmol/L NaHCO3.The body weight,length,and the SGR of juveniles reared in water with 25.10 mmol/L NaHCO3were significantly lower than in the remaining groups(P0.05).The largest final body weight,body length,SGR,SGRW,and FCE were in fish reared at 15.83 mmol/L NaHCO3.The fish reared at 63.12 mmol/L NaHCO3 had the lowest values for all indices.Rearing in water with NaHCO3 levels 39.80 mmol/L had negative effects and the optimal alkalinity for growth was 20.57 mmol/L.Observation of gill microstructure revealed hypertrophy in the chloride cells,and both hypertrophy and edema in the epithelial cells as salinity and alkalinity levels increased,thereby affecting the growth of the fish.In conclusion,the salinity should bebelow 6.1 or the alkalinity should be below 25.10 mmol/L in the Barbus capito larvae culture.