Report on the induced maturation and ovulation of milkfish (Chanos chanos) reared in tanks

Abstract

The milkfish (Chanos chanos [Forskal]) is one of the most important cultivation fishes in Southeast Asia. Since 1970, Tungkang Marine Laboratory (TML) has embarked on a long-term program in broodstock maintenance and artificial propagation with the goal of supplying adequate fry for milkfish farming. In the past three years, the histological study of gonadal development and the experiment on inducing maturation and ovulation of adult milkfish with hormonal injections were carried out. It was found that 5- or 6-year-old tank-reared fish could reach full maturity after hormonal treatment. Sperm were always found in males with Gonadal Somatic Index (GSI) larger than 0.20, with or without treatment. All of the ovarian oocytes of three female spawners with GSI of 11.23, 8.12 and 10.70 reached mature stage after treatment, and average diameter of the eggs was 1.16, 0.94 and 1.19 mm, respectively. One female spawned naturally after one injection, and released hydrated eggs measuring 1.08 mm in diameter. However, the eggs were not fertilized.

Pituitary gland homogenates of both salmon and mullet, human chorionic gonadotropin (HCG), and Puberogen plus vitamin E used in the present experiment seemed more effective in stimulating gonadal development when ovarian oocytes were beyond the tertiary yolk stage, i.e., the oocyte sizes were larger than 0.70 mm in diameter.

Although most of the treated females failed to ovulate, they were still prospective spawners. The success of artificial propagation with tank-reared spawners is anticipated in the near future.