The effects of photoperiod and density of postlarvae on settlement and metamorphosis of the native abalone, Haliotis asinina were determined in two separate experiments. Abalone larvae were hatched from spontaneously spawned eggs of tank-held broodstock. Experiments were conducted in static water conditions within a 10 day-period. Post-larvae held under at 24 h light regime showed higher settlement rates (mean: 12 %) than did larvae held at different light-and-dark periods (range: 3-9 %). Larvae kept in the dark had the lowest survival (3 %). Postlarvae stocked at lower stocking densities of 100 and 150 l ^-1 had higher settlement rates (12-12.5 %) than postlarvae stocked between 200 and 600 postlarvae l ^-1 (1-5 %).

Spontaneous group spawning was monitored in wild-caught (WC) and hatchery-bred (HB) abalone broodstock (Haliotis asinina) held in duplicate tanks at 1:3 (male: female) ratio from June 1997 to January 1999. Abalone breeders (mean SL, wild = 69-79 mm, HB = 68-71 mm) were kept in perforated plastic baskets and fed red alga, Gracilariopsis bailinae, to excess given at weekly intervals. Abalone spawned spontaneously year-round. Water temperature during the study ranged from 26-29 degree C. A total of 139 and 128 spawning episodes were recorded for WC and HB group respectively. Spawning in WC group (mean: 7 ± 0.8) were more frequent in September (1998) and from February to April. Spawning frequency in the HB group (mean: 6.4 ± 1) was generally high during September (1998) until April. Likewise, egg production was highest during these months. Pooled mean survival from trochophore to veligers stage ranged from 7 to 30% (n=36). Potential fecundity was determined in sacrificed group of HB females (n=21) varied from 6,741-11,902 oocytes g ^-1 BW. Mean oocyte diameter ranged from 136 to 150 mu m. Bigger females had higher potential fecundity (range: 6.2 to 11 x 105 oocytes individual ^-1 than smaller females (range: 2.8 to 3.3 x 105 oocytes individual ^-1). The time interval between successive spawning among animals that spawned more than twice during a 5-month period ranged from 13 to 34 days for the small-size group and from 18 to 37 days for large-size group. In separately stocked HB females (without male), instantaneous fecundity was shown to range between 1,500 and 12,300 eggs g ^-1 BW (n=16). In contrast to potential fecundity, smaller and younger individuals gave higher 68-71 instantaneous fecundity (range: >3,000 >12,000 oocytes g ^-1 BW) than the bigger and older individuals (1,500-6,500 oocytes g ^-1 BW).

The intensification of aquaculture in the Philippines has made the use of chemicals and biological products inevitable. A recent survey conducted nation wide among shrimp and milkfish culture facilities revealed the use of more than 100 products for rearing, prophylaxis, and treatment purposes. The most commonly applied chemicals are disinfectants, soil and water conditioners, plankton growth promoters, organic matter decomposers, pesticides, feed supplements, and antimicrobials. All of these are readily available in the market. The dosages, purposes, patterns of use, origins, and manufacturers of these chemicals and biological products are discussed in this paper. The indiscriminate use of chemicals has caused mortalities and morphological deformities in the host and development of antibiotic-resistant bacterial strains. The use of chemicals in aquaculture also poses dangers to public health. Government policies regulating or prohibiting the use ofcertain chemicals for aquaculture have helped curtail the destructive consequences of chemotherapy. Moreover, research institutions have geared their studies towards discovering environmentally safe drugs and other alternatives to disease control. However, these efforts will be futile unless a strong and aggressive campaign on the cautious and restricted use of drugs in aquaculture is conducted among shrimp and fish farmers, drug manufacturers and suppliers.

Throughout the tropics, mangroves are being destroyed at an increasing rate for the development of aquaculture ponds. In the Philippines, for instance, mangroves were about 400,000 to 500,000 ha in 1918 but were reduced to 100,564 ha in 1987. On the average, about 3,500 ha of mangroves are lost every year in the country to accommodate the aquaculture industry (Baconguis et al., 1990). Loss of mangroves means loss of habitat, fishery, income, and livelihood for many coastal inhabitants. The annual catches of major fishing grounds in the Philippines were positively correlated with the areas of existing mangroves (Bagarinao, 1998). Restoration programs of the government such as mangrove reforestation and afforestation were attempted but could not catch up with the unending destruction. An alternative source of income which is directly supportive of resource management was therefore proposed to mitigate ecosystem degradation with the fisher communities in mind. Fishing villages in the Philippines are generally located in the fringes of arable land along coastal plains and are dependent on fishing as a source of income. The common denominator of these villages is the presence of large areas of tidal flats with existing mangroves. To utilize the aquaculture potential of these mangroves, aqua-mangrove integrated farming development projects were introduced to provide alternative livelihood for the fishers in the village. This integrated approach to conservation and utilization of mangrove resource allows for maintaining a relatively high level of integrity in the mangrove area while capitalizing on the economic benefits of brackishwater aquaculture. The projects took off from the concept of co-management, that is, taking into account the partnership between the local community, the local government unit, and the SEAFDEC Aquaculture Department (SEAFDEC/AQD) in the management of the project.

Scylla serrata larvae were reared in 3 L plastic containers and fed various amounts of artificial diets (AD) with or without natural food (NF: Brachionus rotundiformis and newly-hatched Artemia). The amounts of AD fed alone to zoea in treatments (T) 1 to 4 were as follows: 1) 2.0 mg/L/day + 0.25 mg/L/day increment/substage; 2) 2.0 mg/L/day + 0.5 mg/L/day increment/ substage; 3) 4.0 mg/L/day + 0.5 mg/L/day increment/substage; 4) 4.0 mg/L/day + 1.0 mg/L/day increment/ substage. NF were given in addition to the respective amounts of artificial diet in T5, T6, T7 and T8. T9 served as the control (NF only). Based on three experimental runs, only larvae in T5, T6, and T9 survived until the megalopa stage. Thus, only these three treatments were compared in succeeding experiments using a commercial shrimp diet in 250 L fibreglass tanks. Of the three runs conducted using a commercial diet, two runs showed significant differences (P<0.05) in survival. T5 gave higher survival (3.71% and 1.33%) than T9 (1.84% and 0.45%) and T6 (1.37% and 0.45%). Population development index did not differ among treatments in three runs.

The effects of three levels of stocking density (0.5, 1.5 or 3.0/m2) and monosex culture (male or female) on the growth, survival and production of Scylla serrata were investigated. Juvenile crabs were stocked in 150 m2 enclosures in earthen ponds with Gracilaria as shelter and fed a mixed diet of 75% fresh brown mussel flesh and 25% fish bycatch. There was no interaction between stocking density levels and monosex culture (P<0.05) so the data were pooled for each sex or stocking density treatment. Results showed that highest survival was obtained from a stocking density of 0.5/m2 (P<0.05). Crab growth at different stocking densities was not significantly different (P>0.05). Highest return on investment (ROI) and lowest production costs were attained from 0.5/m2. Partial budgeting analysis showed that no net benefit accrued from stocking beyond 1.5/m2. Male crabs attained significantly better (P<0.05) final weight and specific growth rate than female crabs. Length, width, survival and production between male and female crabs were not significantly different (P>0.05). Male and female monoculture gave high net revenue and ROI of more than 100 but male monoculture is more profitable. Overall the results suggest that the culture of male or female mud crabs at 0.5–1.5/m2 with Gracilaria is economically viable.

Feeding experiments were conducted to determine the effect of diet on reproduction of pond-sourced unablated and ablated Scylla serrrata broodstock. Broodstock were fed either natural food (T1) consisting of mussel, squid, fish by-catch, a combination of natural food and formulated diet (T2), or formulated diet (T3). After 120 days of culture, best broodstock response in terms of total spawnings, spawnings with hatchings, number of eggs per g body wt (BW) of female, egg fertilisation rate, and total zoea produced was obtained in T2 and poorest response was in T1. Broodstock in T3 gave intermediate values among the treatments. Larval quality measured as zoea growth index and broodstock survival was also highest in T2. Results showed that combination diet feeding improves the reproductive performance and larval quality of unablated and ablated females compared with those fed on natural food or artificial diet alone. Latency period from stocking to maturation and spawning was shorter in ablated than in unablated females. Rematurations were observed both in unablated and ablated females in all dietary treatments.

Pioneering research on shrimp diseases in the Philippines was spearheaded at the Aquaculture Department of the Southeast Asian Fisheries Development Center at Tigbauan, Iloilo in 1975. Investigations initially covered diseases of hatchery-bred shrimp fry and extensively-cultured shrimp juveniles which eventually extended to semi-intensive and intensive cultured shrimps. To date the following diseases of Penaeus monodon and other Penaeids in the Philippines were reported: Monodon Baculovirus (MBV) Disease, the Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) Disease, Hepatopancreatic Parvo-like Virus (HPV) Disease, Yellow-head Virus (YHV) Disease, Spawner-isolated Mortality Virus Disease, Luminous Vibriosis, Other Vibrio Infections, Shell Disease, Filamentous Bacterial Disease, Chronic Soft Shell Syndrome, Blue Disease, Red Disease, Ascorbic Acid Deficiency Disease, Parasitic Infestations, Acid Sulfate Disease and Hypoxia. A summary of research findings on these diseases, their prevention and control are presented.

Spatial distribution and community structure of zooplankton species and its relationships with the environmental parameters (temperature, salinity, and turbidity and phytoplankton distribution) in some sandbanks of the Belgian coastal zone was carried out by the use of Two-Way Indicator Species Analysis (TWINSPAN) and Canonical Correspondence Analysis (CANOCO). There were 49 zooplankters identified all over the three sandbanks. Crustaceans was the most dominant sub-phyla represented mostly by copepods. Other members of plankton community were also present like cladocera, appendicularia, pteropoda and the larger omnivores and carnivores such as hyperiid, amphipod, chaetognath, ctenophore and fish larvae. TWINSPAN did not show a distinct division of the sandbank stations because of the presence of three dominant copepod species (Temora longicornis, Pseudocalanus elongatus and Centropages hamatus) in the three sandbanks. Canonical correspondence analysis (CANOCO) showed that species distribution of zooplankton was significantly affected by the environmental variables. This was due to lower salinity values observed around Buitenratel sandbank than Gootebank and Westhinder sandbanks. Two-Way Indicator Species Analysis analyzed spatial distribution and community structure of zooplankton species over the three sandbanks of the Belgian coastal zone based on species abundance. Canonical Correspondence Analysis (CANOCO) on the other hand, gave an idea on how far these subgroups were related to environmental variables.

The digestibilities of animal and plant protein sources were determined for P. monodon (30 ~ 40 g wet weight). Protein sources were incorporated in complete diets containing the indicator, chromic oxide at 1.8%. Casein, (APDC=97.9%) was highly digested. The APDC values of shrimp meal (Acetes sp.) and squid meal were 95.4% and 96.0%, respectively. These values did not differ from those for plant protein sources such as soybean meal (93.4%), yeast (93.0%) and wheat germ meal (91.9%). Fish meal (60.75%), meat and bone meal (73.8%) and copra meal (75.2%) had significantly lower APDC values while shrimp head meal and testis meal were digested at 89%~90%. Assimilation (U¹) of dietary organic matter by the ash-free method ranged from 58.3%~90.19%. The TPDC of feedstuffs were generally higher by about 5% than the APDC. A highly positive correlation was observed between APDC and ADMDC (r=90). Protein content of all diets which ranged from 12.9%~60.18% showed no correlation with APDC, TPDC, ADMDC and U¹. This study showed that the shrimp has the capability to similarly digest plant and animal protein sources.