Studies on some aspects of biology with special references to induced spawning of thai pangas (Pangasius sutchi Flowler, 1937)

A total number of 88 fishes Thai pangas were conducted for induced spawning experiments. Among them, 30 mature Pangasius sutchi were conducted for the length-weight relationship, 25 matured females for the fecundity and 33 fishes (12 males and 21 females) for induced spawning experiments. The total-standard length relationship curve shows a straight line with a strong correlation (r = 0.986 and 0.987). The length-weight relationship was best expressed in the logarithmic scale and follows the cube law. The absolute fecundity was ranged from 122000 to 241900 oocytes with an average of 181950 oocytes per female. In the single-dose injection pituitary extract (PG), the average number of eggs release was 182075 ± 95136. The rate of fertilization was 69 to 95%. The average rate of hatching was 70.04 ±34.73%, which was higher in the peak-spawning season with PG treatment. In the double-dose experiment with HCG, the number of eggs released was 150,000 to 200,000 and the fertilization rate was 73.00±40.99% and the hatching rate was 58.33±32.78%. With the double dose of PG, the number of eggs released was 160000 to 260000. The fertilization rate was 76.50 ±42.68 % and the hatching rate was 58.75 ±32.83% with the double dose PG extract. In these experiments, it was established that the PG was more suitable and economical than HCG.