Studies On The Toxicity Of Carbon Dioxide System To Seawater Fish

The tolerance of seawater fish Japanese sea bass ( Lateolabrax japonicus) and black rockf ish(Sebastodes juscescens)to pH and alkalinity is studied through the experiment of acute toxicity. The median lethal concentration values are obtained by the method of probability unit. The safe concentrations of alkalinity, C032- and HC03- are obtained. The signification of pH and alkalinity is estimated with analysis of variance. The major mortality factors in different range of pH and alkalinity arediscussed. The main contents are as follows:l.When Alk is steady at 6.5 + 0.5 mmol/L, the 24-,48-,96-hour LC50 ofpH are 9. 55, 9. 42, 9. 32 to juvenile Japanese sea bass, and 9.87, 9. 48, 9. 38 to black rockfish. When Alk is at a constant level, the toxicity of pH to fish increases with the progressive increase of pH or time.2. When pH is steady at 8.10 + 0.10, the 24-, 48-, 96-hour LC50 of Alk are 60.88, 44.36, 36. 06 mmol/L to juvenile Japanese sea bass, and 75.86, 63.46, 56.42 mmol/L to black rockfish. When pH is steady at 8.40 + 0.10, the 24-, 48-, 96-hour LC50 of Alk are 72. 79, 65. 28, 57. 92 mmol/L to Japanese sea bass, and 69. 47, 59. 37, 51. 96mmol/L to black rockfish. It is obvious that the toxicity of Alk to fish increases with the progressive increase of Alk or time when pH is at a constant level.3. According to analysis of variance of orthogonal test, pH and Alk have signification effects on the mortality rate of black rockfish. Under a certain condition, there is negative correlation between the LC50 values of pH and those of Alk to black rockfish fingerling. The tolerance of black rockfish to Alk or pH weakens as pH or Alk increases. The linear regression equation of 24h is pH=-0. 0229Alk+9. 8463 (N=8, r=-0.9756) , and that of 48h ispH=-0. 025Alk+9. 7519 (N=8, r=-0. 9689) , and that of 96his pH=-0. 0273Alk+9. 7352 (N=8, r=-0.9740) .4. The 24-, 48- and 96h-LCM values of C032~to Japanese sea bass are 6. 23, 5. 22 and 4. 97 mmol/L. The SC of CO,2' is 1. lOmmol/L The LCM values of C032~to black rockf ish are 9. 88, 8. 28 and 7. 13 mmol/L. The SC of CO,2" is 1. 74mmol/L The LCso values of HC03~ to juvenile Japanese sea bass are 52.14, 37. 96 and 30.84 mmol/L The SC of HC03" is 6.04 mmol/L. The LCa, values of HC03" to black rockf ish are 66. 03, 55. 21 and 49. 08 mmol/L The SC of HOV is 11. 58 mmol/L. The LCM values of COj to Japanese sea bass juvenile are 39. 58, 28. 51 and 14.02 mg/L. The toxicity of COsto fish is more acute than that of HC03~, and the toxicity of C032~ is 6~8 times than that of HOV.5. According to the LCso and SC values of pH, Alk, C02, HC03" and C032~, the major mortality factors which effect survival of fish are obtained in different range of Alk and pH.At lower Alk (12mmol/L), the major mortality factor is C02on lower pH interval (pH<7. 6), next is H+. On higher pH interval (pH>8. 7) the major mortality factor is OH", next is C032~.When Alk is between 12 and 20mmol/L, the major mortality factor is C02 on lower pH interval (pH<7. 8), next is HC03~ and H+. Those are HC03~ and C032~whenpH is between 8.1 and 8.7. Those are C032~ and OH" on higher pH interval (pH>9. 0).The tolerance of seawater fish to pH and alkalinity are obtained through the experiment. It provides an academic basis for water quality modulation of seawater fish culture.