A new species of penaeid prawn, Metapenaeus philippinensis from the Philippines is described in detail and compared with the closely related species, M. ensis. The petasma of the new species which superficially resembles that of M. ensis is markedly different in details; the distomedian lobes have rounded postern-lateral comers and the denticles are borne on a crescentic ridge on the disto-medial aspect of the lobes. The thelycum is also distinctive, with lateral tufts of setae and two conical pillar like prominences at the posterior end of the lateral plates and a characteristic median plate which is broader posteriorly than anteriorly. The new species is devoid of dorsal carina on the first three abdominal segments.

The toxicity of malachite green to the larvae of the jumbo tiger prawn Penaeus monodon was determined in a static bioassay. Daily larval death was directly proportional to the chemical concentration of and exposure time to the dye. Estimates of the TL₅₀ in 24, 48, 72, and 96 h are as follows: 112.80, 30.61, 18.91 and 2.27 micrograms/l for the zoeae; 2502.65, 1105.63, 610.09 and 139.01 micrograms/l for the myses; and 2900.17, 339.28, 70.85, and 66.60 micrograms/l for the postlarvae. No adverse effects on the development and moulting of larvae were noted.

Penaeus monodon postlarvae with an average weight of 15.61 mg each were fed fresh brown mussel meat and artificial diets containing casein, shrimp meal, squid meal and Spirulina as protein sources at a daily rate of 20 per cent of their biomass for 10 days. Results indicate that squid meal is best for growth based on weight gain, diet conversion, and protein efficiency ratio. Fresh brown mussel meat was essentiallly comparable to shrimp meal for growth but was inferior based on protein efficiency ratio and survival rate. Both squid meal and shrimp meal appeared to be good protein sources for P. monodon postlarvae.

Pond-reared sugpo (Penaeus monodon Fabricius) females from coastal fry harvested after 4 months were unilaterally ablated and stocked in an indoor concrete tank with an equal number of males. The first two spawnings were obtained 22 d after ablation with the eggs hatching into viable nauplii. Five months (12–15 d from spawning to first postlarva, 14–16 d from first postlarva to coastal fry, and 4 months rearing in ponds) is the shortest age on record at which P. monodon females can be successfully ablated.

Spent Penaeus monodon females were tagged around one eyestalk with numbered brass tags, stocked in a concrete tank with males, and periodically examined for ovarian rematuration over a six-month period (February to August, 1977). The females were either artificially-induced (ablated spawners from concrete tanks and marine pens) or wild spawners. Most of the wild spawners were ablated after spawning; some remained unablated to serve as controls. Out of a total of 349 experimental females, 35 or 10 1% had a second spawning and 5 or 1 4% a third spawning; none of the 74 controls spawned subsequently. The average number of days for maturation and rematuration were: ablation to first spawning, 22 6 days; first spawning to second spawning (for females ablated before the first spawning), 11 days; first spawning to second spawning (for females ablated after the first spawning), 15 days; and second spawning to third spawning, 10 4 days. Fecundity of rematured spawners is comparable to that of first spawners; there is insufficient data on hatching rate and fry survival.

Preliminary experiments resulted in successful spawning of captive stock of the prawn Penaeus monodon, or “sugpo”, to complete the life cycle and produce a viable F1 generation of larvae. Gonadal development was induced using eyestalk ablation techniques on sexually mature females. Removal of one eyestalk was found to be sufficient to induce gonadal development, whereas bilateral ablation indirectly resulted in high mortality of the treated females. By comparison, successful spawning had not occurred in unablated animals after 9 months. Fry hatched from wild adult stock and reared to 25-day postlarvae were further impounded in brackishwater experimental ponds and reared for 4 months. A transfer of 1 500 animals were then made to marine pens. After a further 10 months, 600 animals were selected for the experiment; healthy females were ablated unilaterally and placed with 100 males for a further 9 months. Of the remaining 400 specimens, 200 were used as controls and the remainder ablated bilaterally, Seven of the 23-month old females with one eyestalk removed had spawned successfully by January 27, 1976. Egg numbers, hatching rate and larval survival compared favorably with data obtained from females of oceanic origin. It is not known if the success of the experiment was entirely due to the effect of ablation or to the choice of a suitable environment. Work is continuing to induce gonadal development under more closely controlled conditions to overcome the inadequate and unreliable supply of spawners.

The age-old problem of finding a cheap suitable food for Artemia is finally solved with rice bran, in fact a waste-product which is available at a very low price in many countries all over the world.

The economic viabilities of two types of commercial hatchery milkfish (Chanos chanos) fry operations were assessed and compared. Based on the actual cost of input, the physical facilities, and the potential production yields, four commercial hatcheries previously used for shrimp (Penaeus monodon fry production were classified as either largeor smallscale operations. Cost-return analysis revealed high profits for both types of operation. The return on investment (54-61 %) and the payback period ( approximately 1.5 years) were comparable between the two types, although a large-scale operation (476 %) had double the working capital return of a small-scale hatchery (221 %). Benefit-cost analysis over a 5-year period also revealed positive and above-baseline discounted economic indicators [net current value = 0.2-2.2 million Philippine Pesos (1 US Dollar = 25 Philippine Pesos); internal rate of return = 88-107 %]. The net benefit-cost ratio of a large-scale operation (2.0) was higher than that of a small-scale hatchery (1.4), suggesting a slight edge in the investment viability of a large-scale hatchery. Compared with a large-scale operation, a small-scale hatchery was more sensitive to changes in the acquisition price of eggs or newly-hatched larvae and in the price of selling hatchery fry. Both types of operation are viable nonetheless when the acquisition cost is P6000 per million eggs or larvae and hatchery fry are sold at P0.50 each. Together, profit and investment in milkfish hatchery fry production appear viable, making milkfish an alternative commodity for production in many abandoned shrimp hatcheries. The limited availability of spawned eggs and larvae for rearing and the quality of hatchery fry are issues requiring urgent attention.

Oocyte and blood samples were taken from gravid female catfish Clarias macrocephalus at 4-h intervals to monitor the stage of oocyte development and serum steroid hormone profiles after injection of luteinizing hormone-releasing hormone analogue (LHRHa) and pimozide (PIM) during the off-season (February) and the peak of the natural breeding period (August). Results showed that the onset of final oocyte maturation (12h) and ovulation (16h), and levels of serum estradiol-17β (E₂) did not vary with season in LHRHa+PIM-injected fish. In February, ovulated eggs were stripped from three and two hormone-treated fish at 16h and 20h post-injection, respectively. In August, ovulation was observed in all hormone-treated females (n=5) at 16h post-injection but stripping of the eggs was possible only 4h thereafter. Serum E₂ levels were significantly different only with varying time post-injection; a marked increase occurred at 12h, but the elevation was higher in fish induced to ovulate during the peak (16.8ng/ml) than off-season (7.7ng/ml). Hormone-treated fish showed higher serum testosterone (T) levels during the peak season (17-23ng/ml) than those injected during the off-season (10-20ng/ml) at 4-12h post-injection. Serum 17α, 20β-dihydroxy-4-pregnene-3-one (DHP) levels of hormone-treated fish during the off-season were only about half the level (0.29 and 0.52 ng/ml) of those treated with the same hormones during the peak season (0.54 and 0.9ng/ml) at 8 and 12h postinjection, respectively. Development of oocytes and serum steroid hormone profiles after LHRHa+PIM-induced ovulation provide basic understanding of the processes that mediate final oocyte maturation and ovulation in captive C. macrocephalus.