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.

Seasonal reproduction of the climbing perch Anabas testudineus in the Candaba wetland, Philippines, is described. Monthly specimens were collected, gonads and viscera excised, and the gonads histologically examined. Low mean female gonadosomatic index [GSI (%)] from September to February (0.3–2.1 %) increased in March (8.7 %), peaked in May (10.9 %), and declined in June (3.3 %), but increased again in July and August (8.3–5.5 %). Male GSIs (at least 1 %) were low from September until May, increased in June (2.5 %), and then declined thereafter. All the six oocyte and four spermatogenic cell development stages were observed in the gonads throughout the annual cycle. The ovary was dominated by primary growth oocytes (chromatin nucleolus, perinucleolus) from August to February (77–90 %), but yolky oocytes (previtellogenic, vitellogenic) comprised 15 % to 28 % of the ovary from March to July. Mature oocytes were present for most of the year, comprising 40 % of the total oocytes in March-April, peaking in May (50 %), but declining to 30 % in June–July. Spermatozoa consistently dominated the testis throughout the annual cycle, particularly in November and March (58 %). Food intake in both sexes was generally low during the dry season (December–April) when gonad activity was also low, but started to increase at the onset of the wet season (May–November) when gonad activity began to peak. These results demonstrate that the climbing perch gonads exhibit asynchronous development, allowing a protracted breeding season with intense gonad activity timed at the onset of the wet season, concurrent with increasing food intake through the rest of the season.

Because of high mortality recorded in pond-reared shrimps due to luminescent vibriosis infection, a study was conducted to determine if postlarvae (PLs) could be major sources of luminescent bacteria (LB). Batches of hatchery-reared (PL12 to 18) and wild-caught Penaeus monodon PLs were examined to determine their bacterial load. Results show that although all PLs have associated Vibrio spp., not all of them harbored detectable levels of LB. Fifty eight percent of wild-caught postlarval batches did not have associated LB compared with only 23-44% of hatchery-reared postlarvae. A significant difference in quantitative LB load was noted between hatchery reared and wild-caught PLs with the former harboring up to 3.0 x 10⁵ cfu LB/postlarva. Wildcaught PLs had only up to 3.5 x 10² cfu LB/postlarva. Antimicrobial sensitivity tests using disc diffusion method show significant resistance to Chloramphenicol and Oxytetracycline among isolates from hatchery-reared PLs (33 and 44%) compared with bacteria from wild-caught PLs (3 and 6%) and near shore seawater (0 and 12%). The differences between the quantitative and qualitative bacterial flora of hatchery-reared and wild-caught PLs may have contributed to the occurrence of luminescent vibriosis in grow-out ponds, which generally make use of hatchery-reared postlarvae.

This case study presents the successful practice of sustainable intensification of milkfish aquaculture in marine fish cages under semi-intensive grow-out conditions in the Panabo City Mariculture Park (PCMP) in Davao del Norte, Philippines. Established in 2006, PCMP became operational through the promulgation of a City Ordinance declaring 1 075 hectares of municipal waters in Panabo City as a Mariculture Development Zone/Park. The operations of PCMP were so successful that in just five years it became the third largest among the 63 operational MPs in the Philippines during 2011, with 86 private investors-locators operating a total of 322 units of cages. At present, a total of 372 units of fish cages are operating in the mariculture park (MP). A combination of factors contributed to the successful operation of PCMP, but the success is usually attributed to the effective partnership between the government (both local and national) and the private sector. The Comprehensive MP City Ordinance that governs the PCMP is strictly implemented and includes, among others, the tenurial rights and access to locators. Regulations on distances between cages are strictly enforced and security measures in the total area are jointly undertaken by the government and the locators. The national government, through the Bureau of Fisheries and Aquatic Resources-National Mariculture Center (BFAR-NMC), provides technical support in all aspects from stocking to harvest during the production cycle. BFAR-NMC staff conduct regular periodic sampling of the stocks and compute feeding rates for the stocks which are implemented by the technicians/caretakers. Likewise, BFAR-NMC staff regularly monitor the water quality of the MP and the health status of the stocks. Since it became operational in 2006, the PCMP did not report a single incident of mass fish kill, which indicates that the technical guidelines of MP operations are strictly followed. Workers are trained and organized into groups by BFAR-NMC such as caretakers, cage framers, netters, harvesters, fish processors, and others, and actively participate in discussions related to MP operations to ensure protocols are properly followed. Harvests of stocks are done by skilled workers trained by BFAR-NMC, all done in the “Bagsakan Center” or fish landing area and are well-coordinated. The support facilities in the fish landing area are provided by both the local and national government and the PCMP Producers Association. The operators provide complete data for their operations to BFAR-NMC for record keeping. The strong partnership between the national government through BFAR-NMC, the local government unit, the investors, as well as the acceptance and support from the community for the PCMP is the hallmark of its success.

The oxygen consumption rate (OCR) and ammonium excretion rate (AER) of a tropical sea cucumber, Holothuria scabra, were determined in laboratory experiments. OCR and AER exhibited a significant negative correlation to body weight (BW), expressed as a power function of \(\mathrm{BW:}\; \mathit{OCR} = 0.09 \times BW^{-0.58}(\mathrm{mgO_{2}/g/h, r^{2}=0.89, n=15})\) and \(AER = 0.38 \times BW^{-0.19}\) \((\mathrm{\mu\text{molN/g/h}}, \mathrm{r^{2}=0.54}, n=15)\). These values were comparable to those in previous studies on other sea cucumber species. The OCR of shrimp tank sediment was reduced to less than half \((4.5 \pm 0.3 \mathrm{\;to\;} 1.0 \pm 0.1\;\mathrm{mgO_{2}/gdry/h)}\) by the ingestion and excretion process of H. scabra. Acid volatile sulfide (AVS-S) concentration was also decreased to less than half (0.67 to 0.31 mgS/mgdry); despite the low reduction rates of organic carbon and nitrogen contents (0.19 to 0.14 mgC/mgdry and 0.022 to 0.019 mgN/mgdry, respectively). These results suggest that components in the sediment with high oxygen consumption potential were removed by H. scabra. These findings also provide fundamental information with which to evaluate the quantitative role of H. scabra in polyculture with shrimp.

The growth of the juvenile sea cucumber, Holothuria scabra, was studied under captivity to elucidate the growth variation pattern and determine the best-fit growth model to estimate age- and size-specific growth rates. Individual growth was extremely variable, with some individuals below the mean initial weight and some expanding their original body length (L) and weight (W) by up to 6.4 and 156 times, respectively; during 84 days of culture starting at 127 days of age. Some of the smallest individuals showed a higher condition factor than larger individuals in the presence of ample food, indicating that lack of food may not be the only impediment to growth. Among the three growth models compared (von Bertalanffy, Gompertz and logistic), the Gompertz model was considered optimal to express H. scabra growth; both in L and W. The age- and size-specific daily growth rate for L and W up to 365 days of age, as estimated by the Gompertz model, had a range of two and nine orders of magnitude in L (0.035 – 0.96 mm/day) and W (3.4 × 10^-7 – 3.5 g/day), respectively. Use of the Gompertz model over the linear model, which tends to overestimate growth rates, is encouraged to estimate the growth of H. scabra more accurately.