Browsing by Author "Duray, Victoriano M."
ArticleFemales of Siganus guttatus reared to sexual maturity in canvas tanks were induced to spawn by using human chorionic gonadotropin (HCG, Ayerst) at 500 IU/fish or about 2 IU/g body weight. The amount of HCG used depended on the initial mean egg diameter; the smaller the diameter, the more HCG was used. Fish with oocytes characterized by germinal vesicle migration (mean egg diameter ≥ 0.47 mm) spawned without HCG injection. Fertilization and hatching rates for both treated and untreated fish were more than 90%. The larvae were reared to metamorphosis using rotifers from day 2–17, rotifers + newly hatched Artemia nauplii from day 18–20 and rotifers + newly hatched Artemia nauplii + artificial feed from day 21–35. In addition, Isochrysis galbana was introduced to the rearing tanks from day 1–10 and Chlorella sp. and/or Tetraselmis sp. from day 1–35. Survival rates of larvae tended to be lower as the broodstock became older.
ArticleExperiments were conducted to determine the tolerance of Siganus guttatus eggs to salinity changes. In the first run, the female was induced to spawn spontaneously by using human chorionic gonadotropin. The fertilized eggs were transferred to seawater of salinities ranging from 8 to 40‰ either at the blastomere or at the gastrula stage. In the second run, the eggs were stripped from the female and artificially fertilized following the dry method. Results indicated that eggs transferred at gastrula stage were more tolerant to salinity changes than those transferred at the blastomere stage. Hatching occurred at all salinities but was highest at 24‰. Percentage of viable larvae was highest at 24‰ and lowest at 8‰. The larvae that hatched at low salinities were relatively longer than those that hatched at ambient and higher salinities.
Induced breeding and larval rearing experiments with milkfish Chanos chanos (Forskal) in the Philippines Salmon pituitary homogenate was used alone or in combination with human chorionic gonadotropin, to induce spawing in captive and wild adult milkfish at ambient temperature (26–30°C) and salinity of 34%.. Healthy or slightly injured females having oocytes with a minimum mean diameter of 0.66 mm could be induced to spawn in captivity using a total dose of 20 mg SPH/kg + 3000 IU HCG/kg given in two injections. Badly injured females did not respond readily to the hormone and required more than two injections to induce ovulation. Milkfish larvae were reared successfully to metamorphosis using only Chlorella-fed rotifers during the first 10 days. Survival rates were greatly improved when, aside from Chlorella and Chlorella-fed rotifers, Isochrysis galbana and Tetraselmis chuii were added to the rearing tanks.