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.

Ionic composition of the seminal plasma and factors that initiate sperm motility in the freshwater Asian catfish Clarias macrocephalus, were examined to develop an artificial seminal plasma (ASP) that can be used to dilute milt. The optimum ratio of milt:ASP that can reversibly activate the sperm and milt–ASP:ovulated eggs that will result in high fertilization rates were further determined to minimize the number of males to be sacrificed during artificial insemination. Seminal plasma of C. macrocephalus contained 17.8±0.1 mM/l potassium, 164.4±0.6 mM/l sodium, 8.4±0.0 mM/l calcium and 1.6±0.0 mM/l magnesium, and had an osmolality of 269.0±6.4 mOsm/kg, and pH of 7.8±0.2. Sperm motility was highest and longest in all electrolyte (NaCl, CaCl₂, KCl) and non-electrolyte (mannitol) solutions of 200 mOsm/kg. Catfish sperm were motile in all isotonic NaCl–KCl solutions, and were reversibly activated in the ASP (143 mM NaCl, 30 mM KCl, 8 mM CaCl₂, 2 mM MgCl₂, 10 mM HEPES) solutions of pH 6.4–9.4. Altogether, these results suggest that sperm motility in C. macrocephalus was mainly initiated by a decrease in osmotic pressure, rather than ions and pH. High fertilization rates (89–94%) were observed when 10 μl milt, diluted with 1000 μl ASP, was activated with 5 ml of 0.6% NaCl (198.24 mOsm/kg) to fertilize 5 or 10 g of ovulated eggs. Results obtained from the present study provide information on sperm physiology that will lead to more efficient gamete management, and hopefully, an increase in the yield of catfish fry in the hatchery.

One generation of mass selection based on the collimation procedure (early culling of large fry) was applied on Nile tilapia, Oreochromis niloticus L., in net cages set in Laguna de Bay, Philippines. The objective was to test the effectiveness of a low-cost, small-scale broodstock improvement procedure in this culture environment. Directional selection was performed in two steps after initial removal of large fry at 21 days. Selection of parents and testing of the offspring were also conducted in hapa net cages set up in Laguna de Bay. The selection resulted in a significant positive response of 3% relative to the control, which represents a projected 34% gain over 5 years in Laguna cage culture. The realized heritability is approximately 16%.

We report the isolation and cDNA cloning of somatolactin (SL) from rabbitfish, Siganus guttatus. Rabbitfish SL was isolated from an alkaline extract of the pituitary glands by gel filtration chromatography on Sephadex G-100 and reversed-phase high-performance liquid chromatography. SL was monitored by immunoblotting with flounder SL antiserum. The preparation (yield: 0.86 mg/g wet tissues) contained two immunoreactive bands of 24 and 28 kDa on SDS-PAGE. Overlapping partial cDNA clones corresponding to teleost SLs were amplified by PCR from single-strand cDNA from pituitary glands. Excluding the poly(A) tail, rabbitfish SL cDNA is 1605 bp long. It contains a 693-bp open reading frame encoding a signal peptide of 24 amino acids (aa) and a mature protein of 207 aa. Rabbitfish SL has two possible N-glycosylation sites at positions 11 and 121 and seven half Cys residues. The deduced amino acid sequence shows over 80% identity with those of advanced teleosts like sea bream, red drum, and flounder, 76% with the salmonids, 57% with the eel, and 46% with the goldfish SL.

Aquaculture, the farming of shrimp and other useful aquatic and marine plants and animals in artificially confined and tended ponds, pens, and cages, ranks as a phenomenal success story in global food production. In 1975, aquaculture contributed 8% to the overall yield of the world's fish harvest; now it provides more than one-third of the yield. Total aquaculture production in 2003 was 54.8 million metric tons valued at $67.3 billion in U.S. dollars. More than 90% of this output comes from Asia, where aquaculture has its origins and where this month's essay author has lived and worked all of her life. In her essay, Jurgenne H. Primavera, senior scientist of the Aquaculture Department of the Southeast Asian Fisheries Development Center based in Iloilo, Central Philippines, traces the recent history of aquaculture and the socioeconomic and environmental challenges that its rapid growth has wrought, especially for the mangrove ecosystems in which much of brackishwater pond aquaculture occurs. With an eye on all stakeholders, Primavera lays out how aquaculture is now falling short of the goal of sustainability and what steps might be taken to move the industry in that direction.

Netcage culture of Nile tilapia, Oreochromis niloticus L., was conducted in a freshwater reservoir in Dingle, Iloilo, Philippines from February to October 2009 using Test diet (SEAFDEC/AQD) vs. Commercial feed A (Tateh) in the dry season and Test diet vs. Commercial feed B (Hoc Po) in the wet season. Percent crude protein for Test diet, Commercial feed A and Commercial feed B were 34–35%, 27–33% and 25–32%, respectively. Values for crude fat, crude fiber, crude ash and moisture were 6.0–6.5%, 3.5–5.0%, 10–12% and 4–12% for Test diet; 5–7%, 4.0–8.0%, 12% and 12% for Commercial feed A; and 7%, 4%, 12% and 12% for Commercial feed B, respectively. All netcages were stocked with tilapia fingerlings at 15 m^-3 with mean initial weight of 1.2 g and 1.3 g during the dry and wet seasons, respectively. The fish were fed with floating feeds for 87–89 d of culture. For the dry season, tilapia fed with Test diet had significantly higher (P<0.05) average body weight (ABW, 173.0 ± 1.3 g) and % survival (95.3 ± 2.2%) than Commercial feed A (158.0 ± 0.5 g, 92.0 ± 0.6%). Also, the absolute growth rate (AGR) of 1.97 ± 0.02 g d^-1, feed conversion rate (FCR) of 1.29 ± 0.01, final biomass of 154.60 ± 2.4 kg per cage and gross income of PhP 13,914 ± 18 for Test diet-fed tilapia were significantly higher (P<0.05) than those given Commercial feed A. For the wet season, tilapia fed with Test diet were not significantly different (P>0.05) in terms of ABW, survival, AGR, FCR, final biomass and gross income from those fed with Commercial feed B. During the dry season, tilapia fed with Test diet had significantly higher net income compared with those fed with Commercial feed A. There was no significant difference in terms of net income obtained for fish fed with Commercial feed B during the wet season compared with those fed with Test diet. The favorable return on investment (ROI), payback period and production cost per kilogram at 67.83%, 0.62 yr and PhP 46.72, respectively, were also shown by Test diet with a break-even price of PhP 67.55 and a break-even volume of 116 kg per crop. The overall production performance indicated that using cost-effective Test diet with high protein level would be a profitable and sustainable aquaculture venture during the dry season in the Philippines. In the wet season, however, the productive performance of tilapia and the efficiency of artificial feeds tested were relatively the same.