Many teleost fishes inhabiting shallow tropical waters exhibit synchronous spawning around species-selective lunar phases during their spawning season. For example, ovaries of the goldlined spinefoot (Siganus guttatus) develop during a single period each year from June to July in the Ryukyu Islands, Japan, while those of the goldlined spinefoot in the Karimunjawa Archipelago, Indonesia, develop twice a year from March to May, and then again from September to November. Increases in photoperiod and water temperature are possible cues for the initiation of reproductive activity in the populations around the Ryukyu Islands, while the transition between the rainy and dry season may trigger the initiation of reproductive activity in the Karimunjawa Archipelago populations. Moreover, the goldlined spinefoot releases its gametes around the first quarter moon period of the lunar phase, and since the lunar phase is consistent within the Indo-Pacific Ocean, this species can likely perceive cues from the moon and transcribe them as internal signals. In fact, periodical changes in moonlight intensity are expressed as changes in the plasma levels of melatonin, an endogenous transmitter of environmental light/dark cycles. In addition, the mRNA expression levels of clock genes of neural tissues [Cryptochrome (Cry3) and Period (Per2)] change according to changes in the lunar cycle. To date, how the lunar cycle may affect endogenous reproductive processes in fish is not fully understood. However, knowledge of lunar spawning periodicity in commercially important species may help in the management of fisheries resources, determining where and when to prohibit fishing (e.g., time and area closures), as well as promoting efficient aquaculture techniques for inducing synchronous spawning.

In central Philippines, the Aquaculture Department of the Southeast Asian Fisheries Development Center (SEAFDEC/AQD), with strong collaboration and support from the Research Institute for Humanity and Nature (RIHN) of Kyoto, Japan, has been looking into the stock enhancement of tiger shrimp Penaeus monodon in the New Washington Estuary (NWE), province of Aklan, central Philippines. The NWE was a productive fishing ground that has been suffering from degenerating brackishwater fisheries and estuarine environment. Average daily catch declined from 24 kg in 1970s to only 0.7 kg at present. Shrimp fisheries, the most important livelihood, declined in quality and quantity. Tiger shrimps were abundant in catch until the early 1990s when these were observed to decline in volume, replaced by smaller and cheaper species. This was coincidental with the rapid decline in mangrove cover for ponds and huge increase in fishing pressure. It is clear that crucial interventions are required to restore the tiger shrimp fisheries in the NWE in order to increase income of local fishers, while promoting reduction of fishing gears and restoration of mangroves. Stock enhancement of tiger shrimps shows good potential in answering these needs. Site-specific assessments were conducted to evaluate prospects of shrimp stock enhancement in NWE. Conservative simulations of capture of released stocks showed that fishers can increase income by 300%. To decrease fishing pressure in the area, number of gears per fisher may have to be reduced but shrimp catches will be relatively high-priced. Comparative experiments using aquaculture techniques were done to identify strategies especially in the delicate intermediate acclimation rearing. Aquaculture protocols like those for pond preparation were also adapted to be used in a mangrove pen nursery rearing system for shrimps. Supplemental feeding with formulated feeds increased carrying capacity of the culture area, while enhancing growth and survival of stocks. Culture experiments showed that shrimps grow to 0.5 g within 1 mo and >1g in 2 mo. High stocking density of 40-60 shrimps m-2 can be used for <2 mo rearing in a mangrove pen. Release experiments showed that 60-d old shrimps have higher chances of survival when released in the estuaries. With strong support from local communities, government and other sectors, together with effective management and law enforcement, aquaculture-based stock enhancement of tiger shrimps can be a viable intervention to restore livelihood and promote estuarine rehabilitation in the NWE.

SEAFDEC/AQD’s Stock Enhancement Program started in 2001 with the first stock enhancement initiative on mud crab Scylla spp. funded by the European Commission. This was followed by another stock enhancement program in 2005 supported by the Government of Japan Trust Fund with seahorses Hippocampus spp., giant clam Tridacna gigas, abalone Haliotis asinina, and sea cucumbers Holothuria spp. as priority species. This paper discusses the release strategies that have been established for giant clam, abalone and mud crab.

Interest in mud crab aquaculture is increasing throughout the Philippines because of its demand both in local and export markets. Mud crab culture started as low-density polyculture with fish or shrimp using wild crab juveniles and developed to monoculture in ponds and cages. Recently, an integrated mangrove-crab culture system has been practiced. Mud crab species commonly cultured are Scylla serrata, S. tranquebarica, and S. olivacea. The yearly increase in production from 1996 to 2000 (Table 1) may indicate a corresponding increase in the seed collection activity due to greater demand of seeds for stocking. According to many gatherers in the country, there has been a declining volume of all size-classes, from juveniles to adult crabs, gathered from the wild over the last decade. Hence, the development of a commercially viable hatchery technology can play an important role in promoting sustainable crab aquaculture and fisheries management.

The dietary requirements of juvenile sea bass for the essential amino acids, lysine and arginine, were studied. Fish (Initial average weight in Lysine (Study 1) and Arginine (Study 2) experiments were 13.1 g and 2.5 g, respectively) were given amino acid test diets that contained fish meal, zein, squid meal, and crystalline amino acids (about 46% dietary protein) for 12 weeks. Each set of nitrogenous and isocaloric test diets contained graded levels of lysine or arginine. Fish were fed twice a day at 0800 and 1600 h: in Study 1, feeding rate was 4-2.5% of body weight per day throughout the experiment, while in Study 2, fish were fed at a rate of 10% body wt per day during the first four weeks and at 4% body wt per day from 5 to 12 weeks thereafter. The fish were reared in 500 li (Study 1) or 250 li (Study 2) fiberglass tanks provided with flowthrough seawater at 28°C and salinity of 30 ppt. At the end of the feeding experiment, growth, survival, and feed efficiency were determined. Survival was high in fish given adequate lysine or arginine. Mean weight gains were significantly different in fish fed varying levels of lysine or arginine but no significant different in fish fed varying levels of lysine or arginine but no significant differences were found in the hepatosomatic index (HSI), survival, and feed efficiently ratio. From the breakpoint analysis of the growth response curves, the dietary requirements of sea bass juveniles for lysine and arginine are 4.5 and 3.6% of dietary protein, respectively. This information is important in developing research diets and practical feeds for sea bass.

This study was conducted to identify and analyse gender-differentiated adaptation measures and coping mechanisms formulated and implemented by households during Typhoon Frank (international name Fengshen), in barangays Cayos and Bantud Fabrica, Municipality of Dumangas, in the Province of Iloilo, Philippines. The survey was conducted among 120 respondents who were randomly selected from the barangay local government unit. Key informant interviews, focus group discussions and secondary sources were also used to supplement information obtained from the household surveys. Results show that although women and men worked in complementary ways to secure their family assets, gender differences were observed in their preferred adaptation and coping responses. However, statistical analysis shows no significant difference in the responses of women and men relative to the flooding.

This study examined the effect of short-term nitrogen (N) enrichment on Gracilariopsis heteroclada growth and agar quality. Planting materials were soaked in different concentrations of ammonium chloride (NH₄Cl) for 6 h. Total thallus N content was highest in Gp. heteroclada enriched in 300 mg l^-1 NH₄Cl. Growth experiments showed that this enrichment treatment (300 mg l^-1 NH₄Cl for 6 h) increased the growth of Gp. heteroclada (4.22±0.09% day^-1) compared with the control (3.68±0.12% day^-1). Pond culture using enriched Gp. heteroclada resulted in high growth rates (6.14±0.50% day^-1). No epiphyte growth was observed during either the growth experiment or the pond culture. There were no significant differences between the agar yields of the enriched (3.65±0.36%) or control (3.78±0.18%) Gp. heteroclada. Additionally, no significant differences were detected when the gel strength of the enriched (611±22 g cm^-2) and control (587±11 g cm^-2) Gp. heteroclada were compared. The results suggest that the short-term N enrichment method could be an alternative culture strategy to increase Gp. heteroclada production and lower farming costs.

Different approaches are used to prevent and control diseases in aquaculture. Immunostimulation is one method that is gaining popularity and is considered a promising development in aquaculture. Immunostimulants were found to be effective in enhancing parameters of non-specific immunity and resistance to diseases of fish and crustaceans. However, some issues raised on the use of immunostimulants pertains to the short-term nature of immune indices used during efficacy evaluation, possible detrimental effects during long-term administration, or self-damage due to unregulated production of immune effectors. Further testing in large-scale production units has been recommended. This chapter presents the various types and sources of immunostimulants commonly used in aquaculture and in shrimp culture in particular. The effects of each immunostimulant vary depending on its source, dose, route of administration, length of exposure, and the species to which it is administered.

Soy peptide (SP), a soy protein enzymatic hydrolysate, contains bioactive substances that could be utilized as an immune-stimulating feed ingredient. The experiment evaluated the efficacy of dietary SP on promoting growth, and enhancing tolerance and survival to heat stress in juvenile Japanese flounder, Paralichthys olivaceus. Four diets were incorporated with different levels of SP (0, 2, 5, and 10%) and a 6-wk feeding trial ensued. Following the feeding trial, the experimental groups were subjected to heat stress to measure survival rate and heat shock protein 70s (HSP70s) in gill, liver, and skin. Fish fed diets with SP inclusion showed considerable decrease in percent weight gain. Significantly higher lethal time values to 50% mortality (LT₅₀) value were recorded for fish fed 10% SP. Moreover, LT₅₀ values of fish fed 2 and 5% SP were significantly higher compared with fish fed control diet. HSP70s produced in all the tissues were significantly highest in fish fed 10% SP. HSP70s values were significantly higher in fish fed 2 and 5% SP compared with fish fed control diet. A significant reduction in HSP70s among all groups during recovery period was also observed. These results suggest that SP can be used to enhance the immune response and survival of P. olivaceus under heat stress.

The physiological and avoidance responses of juvenile mud crab Scylla serrata to mercury was evaluated by determining mortality using a renewal-type acute toxicity test and assessing crabs’ ability to avoid toxic concentrations. The 96-h LC₅₀ of mercury to juvenile mud crab was computed to be 0.04 mg L^-1. When transferred to clean waters, crabs that survived exposure to concentrations lower than 0.04 mg L^-1 had better chances of surviving than those that were exposed to higher mercury concentrations. Avoidance of juvenile mud crabs to mercury was determined using a fluvarium, which provided the crabs a choice between untreated and Hg-treated waters. Results showed that juvenile crabs were not able to avoid waters that contain 0.1 mg L^-1 mercury, a concentration that was more than twice the 96-h LC₅₀ value. Juveniles previously pre-exposed in 1/50th of the 96-h LC₅₀ value had a higher avoidance threshold and were not able to avoid waters with 1 mg L^-1 mercury. Results suggest that juvenile mud crab is unable to avoid waters containing lethal levels of mercury and this may have potential impacts on crab biomass, distribution, growth, and development.