Hormonal changes accompanying sexual maturation in captive milkfish (Chanos chanos Forsskal)
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Steroid hormone profiles accompanying sexual maturation in captive milkfish are described. There were no significant differences in levels of serum estradiol 17-β (E2) and testosterone (T) between immature male and female fish. Mean E2 levels rose from 0.54±0.11 ng/ml in immature females (Stage 1) to 4.53±1.16 ng/ml in vitellogenic females (Stage 5), while T levels increased from 2.06±0.28 ng/ml to 38.4±9.26 ng/ml. E2 and T levels were positively correlated to GSI and oocyte diameter. In males, serum T levels increased from 2.5±0.40 ng/ml in immature males to 27.73±5.02 ng/ml in spermiating males. A significantly higher T level was found in males with thick and scantly milt (spermiation index, SPI, 2) compared to males with scanty milt (SPI, 1) or males with copious, fluid milt (SPI, 3). Serum levels of E2 and T, and the GSI in females rose significantly during the breeding season (April–June 1983). The levels of both steroids dropped below 1 ng/ml in spent females sampled in succeeding months. In immature males, T levels ranged from 1.11 ng/ml to 2.78 ng/ml and rose significantly to 21.52±8.38 ng/ml during the breeding season when GSI peaked. Serum T levels dropped to around 10 ng/ml in the succeeding months when only spent or regressed males were sampled.
CitationMarte, C. L., & Lam, T. J. (1992). Hormonal changes accompanying sexual maturation in captive milkfish (Chanos chanos Forsskal).
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Conference paperLMB Garcia - In CL Marte, GF Quinitio & AC Emata (Eds.), Proceedings of the Seminar-Workshop on Breeding and Seed Production of Cultured Finfishes in the Philippines, Tigbauan, Iloilo, Philippines, 4-5 May 1993, 1996 - SEAFDEC Aquaculture DepartmentRecent progress undertaken by SEAFDEC/AQD in the development of broodstock of a variety of cultured fish in the Philippines is reviewed. Spontaneous maturation and spawning has been achieved among captive breeders of grouper, milkfish, sea bass, rabbitfish, and tilapia. Hormonal intervention methods have been developed mainly to accelerated final gonadal maturation to synchronize release of mature gametes, and to control sex inversion among hermaphroditic fish such as grouper. These methods entailed the development of gonadal biopsy procedures and hormone administration protocols such as mode on introducing a variety of exogenous hormones to fish, administration intervals, and lately response times.Enhancement of reproduction by improving the diet fed to Nile tilapia, rabbitfish, and milkfish breeders has also been achieved in recent years. Protein or lipid enrichment of the diet may enhance growth of broodstock to subsequently increase reproductive performance and fry survival.Limited success has been achieved with photoperiod manipulation to effect year-round sexual maturation and spawning of milkfish and sea bass broodstock.
Induced gonadal maturation and rematuration in milkfish: Limited success with chronic administration of testosterone and gonadotropin-releasing hormone analogues (GnRH-A) Nine experiments were conducted to investigate the influence of chronic administration of testosterone (T) and gonadotropin-releasing hormone (GnRH) analogues on first maturation of 4- to 6-year-old fish and rematuration of 6- to over 9-year-old spent/regressed fish. Implantation of T or T in combination with luteinizing hormone-releasing hormone analogue (LHRH-A) had no marked effect on maturation rate of 4-year-old milkfish. The percentage of maturing fish was low and similar to controls in Experiment 1 (T, 31–35%; control, 35%) and Experiment 3 (T, 13%; T plus LHRH-A, 28%; control, 22.2%). Most of the 4-year-old maturing fish were males; maturing females were obtained only from the T-implanted groups in Experiment 1. In Experiment 3, T-implanted maturing females were able to retain yolky eggs whereas maturing control females did not, indicating that testosterone may have enhanced vitellogenesis and maintained the integrity of vitellogenic oocytes. Tank-reared maturing 4-year-old females, about half the size of older first maturing females, were induced to spawn. This is the first case of maturation and spawning of 4-year-old milkfish reared in tanks. As in Experiments 1 and 3, the percentage maturation of spent fish in Experiments 7 and 8 was similar for T-implanted and controls. On the other hand, the 4-year-old immature fish in Experiments 2 and 4, the 5- and 6-year-old immature fish in Experiments 5 and 6, and the spent 6-year-old fish in Experiment 9 were immature or regressed throughout. The factors which may have influenced the results of these experiments include age and reproductive history of the fish, timing of hormone implantation, experimental and holding conditions, and stress.
Induced spawning of maturing milkfish (Chanos chanos) using human chorionic gonadotropin and mammalian and salmon gonadotropin releasing hormone analogues The response of maturing female milkfish to D-Ala6-des Gly10 mammalian GnRH ethylamide (mGnRH-A), D-Arg6-des Gly10 salmon GnRH ethylamide (sGnRH-A) and human chorionic gonadotropin (hCG) was investigated. The GnRH analogues and hCG were equally effective when administered by intramuscular injection at doses of 10 μg/kg and 100 μg GnRH-A/fish or 1000 IU hCG/fish. All of the females injected with HCG and 87.5% (⅞) of females injected with GnRH-A spawned. Pellet implantation of the GnRH analogues, however, was less effective based on 100 μg of pellet per fish, which provided from 20 to 36 μg of analogue per kg fish. Fish implanted with mGnRH-A or sGnRH-A showed responses which varied from oocyte hydration to spawning. Only 3⁄7 implanted with mGnRH-A and 1⁄7 implanted with sGnRH-A spawned; in the latter group, the average egg diameter was 11–17% smaller at the time of treatment compared with the other treated groups. Except for one, all fish with egg diameters above 0.65 mm had hydrated/ovulated oocytes or spawned. Females which spawned had egg diameters above 0.71 mm.