Tertiary Yolk Stage Research Articles

養殖１歳マアジの成長，成熟および人工産卵について

The cultural and spawning experiments of jack mackerel Trachurus japonicus (TEMMINCK et SCHLEGEL) from our hatchery were carried out from April 18, 1980 to July 16, 1981. The growth of the cultured fish was considerably high and the fish reached 17.4cm in fork length and 67.0g in weight in average at the end of its first year. The optimal temperature for the growth is ascertained to be between 18° and 26°C. All males are found to be spermiating without hormone injection in April and June, 1981. In some females the ovaries are well enlarged, with maturing eggs deveploped to primary or tertiary yolk stage in May and June, 1981. It is suggested that the cultured fish attained sexual maturity at least at a length of about 15cm in fork length. Twenty six females and 25 males are treated with gonadotropin in May 26, 1981, and placed in a circular tank of about 6 ton capacity at the beginning of the spawning experiment. At the water temperature of about 21°C, spawning began at 32:30 hr, and completed at 39:45 hr after receiving gonadotropin. The fertilized eggs incubated at the water temperature of abuot 21°C began hatching at about 34:40 hr after first spawning.

REPORT ON THE INDUCED MATURATION AND OVULATION OF MILKFISH (Chanos chanos) REARED IN TANKS1

ABSTRACTThe 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.

Oogenesis in a tropical loachLepidocephalus thermalis (Cuv. & Val.)

The development of oocytes has been traced in detail in the loachLepidocephalus thermalis. The various stages of oocytes are described under distinctive stages namely 1. chromatin nucleolus stage; 2. perinucleolus stage; 3. yolk vesicle stage; 4. primary yolk stage; 5. secondary yolk stage; 6. tertiary yolk stage; 7. migratory nucleus stage; 8. pre-ripening stage; 9. ripe egg stage. The yolk deposition is initiated as minute globules in the extravesicular ooplasm. A yolk nuclous is entirely wanting in any stage of oocyte maturation. The origin of new crops of oocytes and the formation of the micropyle are described. Nature of degeneration of unextruded ripe oocytes has been followed.

Reproductive biology of the freshwater catfish, Tandanus tandanus Mitchell, in the Gwydir River, Australia. I. Structure of the gonads

The gross morphology and histology of the gonads of T. tandanus were examined as a preliminary to describing the reproductive cycle of this species in the Gwydir River. The macroscopic appearance of the gonads at different stages of maturity is described. The complicated structure of the testes made it difficult to classify them into well-defined stages of maturity. The relationship between the stage of maturity of the ovaries and the histological changes associated with oocyte maturation was clear cut. Six spermatogenetic stages were recognized; primary germ cells, spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa. The sequence of oocyte maturation was divided into nine stages; chromatin nucleolus, early perinucleolus, late perinucleolus, yolk vesicle, primary yolk, secondary yolk, tertiary yolk, and ripe egg stage. Atresia was observed in some oocytes from the primary yolk stage onwards. The sequence of yolk resorption in atretic oocytes is described.

Induced spawning of the striped mullet Mugil cephatus L.

The response of adult mullet to artificial hypophysalion, immediately before the onset of the spawning migration was studied. Both males and females received intraperitoneal injec‐tions of mullet or salmon pituitary homogenates wth ACTH or Synahorin (APE+HCG) three times per week for 12 days. At the outset, conlrol females were in the tertiary yolkstage with a low mean GSI of 7.6, while males gave thick, non‐dispersing milt. Two of fourfemales receiving one salmon pituitary plus 25 RU Synahorin per injection spawnedspontaneously in laboratory aquaria. Released eggs were buoyant, well formed and had a mean diameter of 570μm. Egg fertility could not be ascertained due to protracted contact with sea water. Spawned females extruded a meinbranous tissue ‘plug’ from the cloaca1 region which was subsequently retracted. The remaining experimental females were refractory to treatment and histological examination of the ovaries revealed a predominance of atretic oocytes. All males were refractory to treatment and milt hydration was not achieved. It is suggested that induction of early spawning is possible especially with higher doses of pituitary homogenates and Synahorin. [Oceanic lnstitute Contribution No, 62 Sea Grant Program, GH‐76].