Ching-Ming Kuo

A procedural guide to induce spawning in grey mullet (Mugil cephalus L.)

Abstract This paper describes the standard practices developed and repeated successfully to induce spawning annually under controlled conditions. The method for sampling ova in vivo and the stages of egg development are described and illustrated. Hypophysation of the gravid females begins when intraovarian oocytes are at the tertiary yolk globule stage. For best results mean egg diameter is at least 600 μ, and preferably larger than 650 μ before inducement begins. For small and less-developed eggs, hypophysation can be induced by varying the dosage and the injection sequence as outlined. Partially purified salmon gonadotropin required to induce spawning is given in two injections, one-third of the total dose is given initially followed by the remaining two–thirds 48 h later. The total dose is inversely proportional to the initial egg diameter of recipient females and varies between 12–21 μg/g body weight. An illustrated diagram for calculating dose level is provide. Fertilization procedures are also described.

Operational procedures for rearing larvae of the grey mullet (Mugil cephalus L.)

Abstract Larvae of the grey mullet Mugil cephalus L. can be reared successfully using careful procedures following induced spawning of the adults with purified salmon gonadotropin or human chorionic gonadotropin. Preliminary incubation of the eggs to the gastrula stage at high density for 12 h at 22°C is preferred, using stirred irradiated seawater (32‰ salinity) and the antibiotics penicillin (80 IU/ml) and streptomycin (0.05 mg/ml). The eggs are transferred before hatching to circular rearing tanks at a density of 250 eggs/l. The mouths of the larvae are open and ossified and the eyes are sufficiently pigmented for the larvae to begin feeding on the third day. The larvae are fed cultured phytoplankton and rotifers supplemented with available natural plankton. Nauplii of Artemia are provided on the seventh day. The migratory behavior of the larvae during early development and their physiology are discussed, being relevant to the procedures and the techniques applied. Mass propagation in large (over 12-ft diameter) circular tanks with total light control is recommended.

The effects of temperature and photoperiod on ovarian development in captive grey mullet (Mugil cephalus L)

Abstract A series of sixteen environmental experiments, conducted under controlled laboratory conditions during the refractory period in the reproductive cycle of the grey mullet, determined the effect of photoperiod and temperature on the vitellogenesis of intraovarian oocytes. Fish subjected to the natural light cycle and ambient water temperatures (24–26°C) served as controls. A classification of stages of vitellogenesis (I–V) is used to determine the percentage composition of oocytes for each fish at intervals throughout the experiment following sampling in vivo. Onset of vitellogenesis is timed by the environmental conditions. A retarded photoperiod, irrespective of preconditioning photoperiod, plays a dominant role in stimulating oocyte growth. Temperature regulates vitellogenesis towards functional maturity. The combination of retarded photoperiod (6L/18D) and constant temperature of 21°C is the most effective for the completion of vitellogenesis of oocytes to functional maturity. Regular injections of pregnant mares serum gonadotropin (PMSG) at 1 IU/g body weight are effective in initiating vitellogenesis.

Recent progress on the control of ovarian development and induced spawning of the grey mullet (Mugil cephalus L.)

Abstract The paper describes some past and current work for the control and regulation of ovarian development. It reports on the induction of ovarian maturation out of season by manipulation of photoperiod and temperature cycle, and recommends conditions of constant temperature control at 21°C and photoperiod of 6L 18D for the best results using fish with oocytes in the refractory period. It also recommends salmon pituitary gonadotropin SG-G100 as the best ovulating agent for reliable results, but suggests further research with alternative gonadotropins and steroids. The paper describes some recent progress with the latter.

Hypotheses for problems impeding the mass propagation of grey mullet and other finfish

Abstract The authors review the problems which, in their opinion, impede successful mass propagation of grey mullet larvae in hatcheries. Individual hypotheses on the reasons for problems associated with oocyte quality, larval foods, bacterial contamination, environmental control and facility design, are discussed.

Annual reproductive cycle of milkfish, Chanos chanos Forskal, in Hawaiian waters

Abstract The monthly mean values of gonadosomatic index (GSI) over a continuous 36-month period show that the population of milkfish, C.chanos Forskal, in Hawaiian waters has a short breeding season between June and August. In these months, the GSIs of the mature individual males are between 3.19 and 5.36%, and of the mature individual females between 7.07 and 9.76%. These figures plus histological data suggest a synchronous spawning behavior for the species. Mature oocytes (stage III) are larger than 0.7 mm in diameter, which increases to about 1.2 mm at the time of ovulation and about 1.35 mm at the time of spawning

Establishing brood stock of grey mullet (Mugil cephalus L.) in small ponds

Abstract A brood stock of 3-year-old grey mullet ( Mugil cephalus L.) was maintained in two small rubber-lined outdoor ponds with circulating sea water. Plastic substrate consisting of weighted polyethylene strips was placed in each pond to increase surface area and provide a stable supply of benthic diatoms, blue-green and filamentous green algae. Water chemistry and daily fluctuations in oxygen, pH and temperature were monitored. Some fish developed air embolisms resulting from oxygen supersaturation, causing mortality. All males and females matured the following year and those not sacrificed for experimental data were induced to spawn by hormone injections.