The effects of three diets (Diet 1 – with vitamin and mineral supplements, Diet 2 – without vitamin and mineral supplements, and Diet 3 – fish bycatch) and monosex culture (male or female) on the growth, survival, feed conversion ratio (FCR), and production of mud crab Scylla serrata were investigated using a 2 x 3 factorial experiment with three replicates per treatment. Juvenile mud crabs were stocked at 1.0·m^-2 in 150 m² ponds and reared for 156 days. Results showed no significant interaction between monosex culture and diets (P > 0.05) so that data were pooled by sex and dietary treatment. Mean final body weight of male crabs (427 g) was significantly higher (P < 0.05) than female crabs (400 g). However, crab carapace length (CL) and width (CW), specific growth rate (SGR), FCR, survival, and production were not significantly different (P > 0.05) between the two sexes. Regardless of sex, crabs fed fish bycatch (Diet 3) gave significantly higher (P < 0.05) mean body weight (435 g) than those fed Diet 2 (395 g). Mean final body weight (410 g) of crabs fed Diet 1 was not significantly different from those fed Diets 2 or 3. The CL and CW, SGR, FCR, survival, and production of mud crabs fed the three diets, however, were not significantly different (P > 0.05). The economic viability of using a diet without vitamin and mineral supplements was comparable to that of a complete diet having about the same cost of production and return on investment of 74 to 75%. The study shows that cost-effective formulated diet could be used as alternative feed for fish bycatch thus saving on feed and storage costs.

Three- to five-day old hatchery-reared megalops (4.0 to 6.4 mg body weight) of the mud crab, Scylla serrata, were cultured to the juvenile stage in 20 m² net cages installed in brackishwater nursery ponds. To establish a suitable stocking density, megalops were stocked at 10, 20, and 30 ind·m^-2 in net cages. Treatments were replicated three times over time. After 30 days of culture, mean survival of juveniles ranged from 48.3 to 53.3% and did not vary significantly (P > 0.05) among the three stocking densities. Similarly, the mean final body weights of juveniles ranging from 2.91 to 3.40 g and mass weights 458.9 to 1066 g did not significantly differ among stocking densities. These results show that stocking of crab megalops directly in net cages in a brackishwater pond is feasible at any of the stocking densities tested.

A protocol for the large-scale rearing of the mud crab Scylla serrata juveniles was developed based on the results of small-scale experiments on feeding and water management. This paper also reports the success in producing the second generation (F₂) crabs. Pond-reared adult S. serrata held in 10 m³ concrete tanks with sand substrates were given fish, mussel, annelids and formulated diet. The zoeae produced were stocked in 1.5 or 10 m³ tanks at 30 to 50 ind-l^-1 and fed 10 to 15 Brachionus rotundiformis ml^-1, 1 to 5 Artemia sauna nauplii ml^-1 and 1.5 to 2.0 g shrimp larval commercial diet-m^-3 day. Water was replaced daily at 30 to 50% of the total volume starting day 3. Megalops were nursed until crab stage either in tanks or in net cages installed in ponds. Crabs were fed mussel or small shrimps (Acetes sp). Hatching occurred 6 to 12 days after spawning at 26.5 to 30.5°C. A female produced 0.42 to 5.23 x 10⁶ zoeae at a time. Mean survival rate from zoea 1 to 3- to 5-day old megalopa was 2.6 ± 0.8% and 32.8 ± 4.8% from megalopa to crab stage. The development from zoea 1 to megalopa required 16 to 18 days. Cannibalism and luminescent bacteria were identified as the major causes of mortality. Highest mortality was observed during the metamorphosis from zoea 5 to megalopa and megalopa to crab 1. First crab stage was obtained 23 to 25 days after hatching. Sorting the crabs during the nursery period minimized cannibalism. Completion of the cycle in captivity was attained in 1997 and 1999 when spawns from pond-reared crabs grew to become the second-generation broodstock. The results point to a minimum age of 7.5 to 9 months at which S. serrata hatched their eggs after rearing from zoea 1.

Two separate experiments were conducted to determine the dietary requirements of juvenile Asian sea bass Lates calcarifer Bloch for lysine and arginine. Fish (average initial weight: lysine experiment, 13.12 ± 0.12 g; arginine experiment, 2.56 ± 0.13 g) were given amino acid test diets for 12 weeks containing fish meal, zein, squid meal, and crystalline amino acids. Each set of isonitrogenous and isocaloric test diets contained graded levels of L-lysine or L-arginine. The feeding rate in the lysine experiment was at 4–2.5% of the body weight day⁻¹, while in the arginine experiment it was at 10–4% of the body weight day⁻¹. The fish (20 per tank, lysine experiment; 15 per tank, arginine experiment) were reared in 500-L fibreglass tanks with continuous flowthrough sea water at 27 °C and salinity of 31 ppt in the lysine experiment and at 29 °C and salinity of 29 ppt in the arginine experiment. The experiments were in a completely randomized design with two replicates per treatment. Survival was high in fish given adequate lysine or arginine. Mean percentage weight gains were significantly different in fish fed varying levels of lysine or arginine. Fish fed high levels of L-arginine suffered high mortalities. No significant differences were obtained in the feed efficiency ratios (FER, g gain g⁻¹ feed) of fish fed graded lysine, although the values tended to increase as the dietary lysine level was increased up to the requirement level. In contrast, in the arginine experiment, significant differences in FER of fish among treatments were obtained; the highest FER was observed in fish fed the diet containing an optimum arginine level. On the basis of the growth response, survival, and FER, the lysine and arginine requirements of juvenile Asian sea bass were estimated to be 20.6 g kg⁻¹ dry diet (4.5% protein) and 18.2 g kg⁻¹ dry diet (3.8% protein), respectively. These data will be useful in the further refinement of practical diet formulations for the Asian sea bass.

Scylla serrata females with initial body weight (BW) of 350 to 400 g were previously raised on a defined diet of 75% brown mussel meat and 25% fish bycatch in grow-out ponds at Molo, Iloilo City, Philippines for 120 days. Crabs were stocked in three units of 4 m diameter concrete indoor tanks at the Crustacean Broodstock Wet Laboratory of SEAFDEC Aquaculture Department in Tigbauan, Iloilo, Philippines. Tanks had sand substrates and were supplied with sand-filtered and chlorinated seawater in a continuous flow-through system with adequate aeration. Each female was provided with individual shelter. Before stocking, crabs were tagged on their carapace and half of the females were ablated while the other half remained intact. Broodstock were fed either T1, natural food consisting of mussel and fish bycatch; T2, a mixed diet of natural food and formulated diet; or T3, a formulated diet. Broodstock reproductive ability was measured as percent spawnings, spawnings with hatching, fecundity or number of eggs per g BW of female, egg fertilization rate and total zoea produced. Larval quality was measured as larval stage index or ability to attain the megalopa stage, the highest larval stage. Females fed on all dietary treatments were capable of maturation and spawnings. However, mixed diet feeding (T2) improved broodstock performance and larval quality over those fed either natural food (T1) or formulated (T3) alone. Eyestalk ablation improved fecundity and produced higher total zoea in T1 and T3 although lower in egg fertilization rate than intact females. All zoea larvae in ablated T2 females were successfully reared to megalops. Overall improvement in larval quality of both ablated and intact females compared with previous studies on wild-caught females was attributed to their dietary history in grow-out ponds. Feeding the females with a suitable diet in ponds enabled them to fortify the reserves of nutrients needed for egg development and improve stability in larval production.

Fallen senescent mangrove leaves from three marine mangrove sites in Panay island, Philippines were collected for observation and isolation of straminipilous organisms. A total of 11 mangrove species were sampled. Halophytophthora species were observed on 7 out of 11 mangrove species sampled, with H. vesicula as the most abundant species observed. Halphytophthora epistomium also occurred abudantly on fallen leaves of Rhizophora apiculata and Sonneratia sp. Thraustochytrids, on the other hand, were observed on all mangrove leaf samples except Aegiceras corniculatum. Schizochytrium mangrovei was the most abundant species observed. Their association and ecological role on the degradation of fallen mangrove leaves is discussed.

Gonadal maturation, spawning, fecundity and timing of reproduction of the snail Cerithidea cingulata in a brackish water pond in Molo, Iloilo, Philippines, are described. Snails 4–41 mm in shell length were sampled monthly from May 1997 to May 1998; 25% were <25 mm, 67% were 20–30 mm, and 8% were >30 mm. The sexes are separate and could first be distinguished at 15 mm. Males are aphallic, have narrower shells than females of the same length, and have bright yellow-orange testes overlying the digestive gland deep inside the shell. Females have more robust shells, an ovipositor at the right side of the foot, and yellow-green ovaries overlying the digestive gland. The sex ratio was one male to two females in the pond population studied. Gonadal maturation was monitored by means of gonadosomatic index (GSI, gonad weight as a percent of visceral weight); maturation stages were based on the gonad appearance (immature, developing, mature) and histology (immature, developing, mature, redeveloping). GSI increased with snail size, and reached 16% in a 33-mm female. The smallest mature males and females were 18–19 mm, and most snails >20 mm were mature, spawning, or redeveloping. Histological sections showed all stages of gametogenesis in mature male snails. The oocyte size-frequency distributions in mature females showed mostly mature oocytes and secondary oocytes, but also oogonia and primary oocytes. GSI and the frequency of snails at different maturation stages varied over the year. Both GSI and the frequency of mature snails were highest during the summer months, April to August. Nevertheless, mature snails occurred throughout the whole year, as did mating and egg-laying. Fecundity (= number of oocytes >70 pμ) increased with size in mature females 2041 mm; an average 25-mm female produced about 1,500 oocytes and larger females produced a maximum of about 2,500 oocytes. Eggs strings laid on the pond bottom were 45–75 mm long; an average 64-mm string contained 2,000 eggs 210+20 pm in diameter. The density of eggs strings was highest (80–120/m²) during March-September. Eggs hatched after 6–7 d into planktonic veligers, which in turn settle on the pond bottom 11–12 d later as juveniles. Juveniles 2–6-mm long were most abundant in the pond during August-October.

Techniques to culture rotifers at high-density (2000 to 20 000 ind./ml) have been developed by utilizing condensed phytoplankton products. Many public hatcheries in Japan have introduced automated systems for culturing and harvesting rotifers. Research has been conducted on the diagnosis of rotifer culture status and chemical treatment for reducing stress on rotifers. Preservation of the resting eggs of rotifers for an extended period or at low temperature (4 °C) for a limited time has become possible. Thus, appropriately sized rotifers can be provided to fish larvae, according to fish species and growth stage. Techniques to identify the genetic status of rotifer strains have yet to be developed. Practices for culturing copepods in Japan have also been summarized.

Gamma-aminobutyric acid (GABA) has been shown to enhance the reproduction of the rotifer Brachionus plicatilis Muller in stressful culture conditions. During the enrichment of rotifers for feeding to marine fish larvae, they are usually stressed as a result of exposure to different marine oils and high population densities. This typically results in decreased rotifer survival, reproduction and swimming activity. In the present study, we used GABA to increase rotifer reproduction and the swimming activity of rotifers in enrichment cultures. GABA treatment 24 h before high density enrichment enhanced reproduction during enrichment culture, but not when carried out simultaneously with enrichment. Swimming activity was not significantly affected by GABA treatment 24 h before or simultaneously with nutrient enrichment.

Wound healing in African catfish, Clarias gariepinus, fed diets supplemented with ascorbic acid was studied under laboratory conditions. Fish weighing approximately 80-110 g were stocked in 500 l aquaria in a static water system and fed one of five test diets containing different levels of microencapsulated ascorbic acid (0, 0.06, 0.10, 0.30 and 0.70 g AsA/100 g feed). After two weeks, all experimental fish were wounded by making a 1 x 1 cm dorso-lateral incision above the lateral line of the fish. Wounded tissues were sampled for histopathological analysis 4, 8, 24, 48 and 96 hours, 6, 8, 10, 12 and 14 days after making the incision. There were significant differences in weight gain, specific growth rate (SGR) and feed conversion ratio among the dietary treatments. Weight gain and SGR of fish fed the ascorbic acid free diet were lower than those of fish fed diets supplemented with ascorbic acid. The wound healing response showed a direct correlation to ascorbate level in the diet. Fibroblasts were present at 96 h irrespective of the ascorbic acid level. As 14 days, fish fed no ascorbic acid had some regeneration of muscle tissues, whereas fish fed diets containing supplemental ascorbic acid had a normal epidermis, dermis and muscle structure. There was no mortality during the experimental period, and fish fed ascorbic acid free diets did not exhibit any deficiency signs. Results of this study indicate that about 0.10-0.70 g AsA/100 g feed is needed for wound repair in African catfish.