Asian moon scallop, Amusium pleuronectes, is among the most common commercially harvested scallop in the Philippines. This study investigated suitable conditioning methods, induced spawning, and documented scallop larval development at the Marine Fisheries Research and Development Center (MFRDC) Guiuan, Eastern Samar. Scallops held in tanks with flow-through water system without substrate yielded high survival rate of 48.06 ± 5.95%. Optimum water temperature was 28-29°C for maintaining scallops. Isochrysis galbana and Chaetoceros calcitrans were suitable microalgal feed for A. pleuronectes consumed at 7,388,888 cells min-1 per scallop. These significant results were applied in maintaining scallops at the hatchery. As a result, scallops with an average 19.8 mm shell length (SL) reached 37.5 mm SL within four months with a survival rate of 96.57 ± 2.04%, average daily growth rate (ADGR) of 0.13 ± 0.04 mm.day-1, and specific growth rate (SGR) of 3.92 ± 1.31%.d-1. Natural spawning was successful under controlled conditions while induced spawning trial through thermal stimulation, food shock, sexual stimulation, and serotonin injection resulted unsuccessful release of sperm and eggs. The estimated number of fertilized eggs per spawning ranged from 0.22-1.4 million. Fertilized eggs appeared spherical and dark in color with 54.2-62.57 µm in diameter. After nine hours, the larvae developed into trochophore stage with 59.08-84.4 µm in length. D-veliger with 120.37-157.07µm shell length developed after 24 hours. Development of the early umbone stage was reached on day 5; and on day 7, the umbo larvae become well-developed with shell length of 135.45-173.36 µm. On day 9, pedi-veligers were observed in the culture. Spat grew 312.41-509.48 µm on day 16 and survived until four months with final shell length of 4-10 mm. For the larval rearing, stocking density of A. pleuronectes larvae observed highest survival rate of 0.04 ± 0.03% at 200 larvae/L, while no larvae survived at 800 larvae/L due to contamination of protozoans in the culture medium.

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Various factors in P. pelagicus seed production and grow-out culture were investigated in this study. Experiments were conducted to 1) compare natural and artificial feeds for larval production, 2) evaluate indoor tank and outdoor net cages as rearing media, and 3) assess different stocking densities for grow-out culture. Growth, development, and survival were assessed for the performance of each variable. (I) In larval production, the development of megalopa larvae into crab instar was synchronous in both natural and artificial feed treatments in a 5-day rearing observation. Crab instars began to appear on Day 4 with 27% composition in both feeds. Although survival appeared to be relatively higher in natural feed (43.96 ± 6.04%), this was not significant from survival in artificial feed treatment (33.33 ± 13.34), (t = 0.726, p > 0.05). (II) In Phase I growout culture, a two-variable design experiment was conducted to assess growth performance and survival of crab juveniles reared in indoor tanks and outdoor net cages at different stocking densities. Specific growth rate (SGR) differed significantly (t = 2.937, p < 0.05) between indoor tanks (6.39 ± 0.24%.d-1) and outdoor net cages (8.31 ± 1.11%.d-1). However, mean survival rate was better in indoor tanks (20.83 ± 9.24%) than outdoor net cages (8.94 ± 3.58% only), (t = 2.938, p = 0.015). In terms of stocking density, SGR was highest in 75 ind.m-2 (7.87 ± 2.44%.d-1). However, growth performance and survival of juveniles among different stocking densities were not significantly different (p > 0.05). Furthermore, two-factor ANOVA results have shown that growth performance of the juveniles was influenced by both the differences in rearing medium and stocking density, but not in terms of survival (F = 0.120, p = 0.888). (III) In Phase II grow-out culture, juveniles attained highest SGR (3.54 ± 0.56%.d-1) at 5 ind.m-2 stocking density. This was followed by 15 ind.m-2 (3.45 ± 2.39%.d-1) and by 10 ind.m-2 (2.33 ± 0.50%.d-1) (p > 0.05). However, survival rate was highest in 15 ind.m-2 (46.67 ± 0.00%), but the differences among other stocking densities were not statistically significant (p > 0.05). Overall, results suggest that artificial feed can be an alternative for Artemia in rearing megalopae to crab instar stage. Stocking density in Phase I and II grow-out culture did not substantially affect growth performance and survival of juvenile P. pelagicus. However, higher stocking density increases incidence of cannibalism among reared crabs.

Spiny lobsters are an important resource of the artisanal fishery in Eastern Visayas, Philippines. It has long been harvested and contributes to the region's local economy. Despite being a high-value species, the spiny lobster resource has not been monitored and regulated for decades. This study aimed to assess the spiny lobsters in Eastern Visayas and provide recent information to support local resource management. Spiny lobsters were assessed from 2018 to 2019 in four major sampling areas in Eastern Visayas: (1) Guiuan and (2) San Policarpo in Eastern Samar province, (3) San Jose in Northern Samar, and (4) Silago-Hinunangan in Southern Leyte. Species composition, relative abundance, geographical and seasonality distribution, and size structure of spiny lobster resource in the region were described. Six species and subspecies of the genus Panulirus were observed in the catch landings: P. penicillatus (65%), P. ornatus (18%), P. versicolor (2.8%), P. femoristriga (5.3%), P. longipes longipes (6.1%), and P. longipes bispinosus (1.7%). Incidental catches (1.3%) of the ambiguous forms of P. longipes were also observed. P. penicillatus were more prevalent in areas exposed to the Pacific, such as Guiuan and San Policarpo, while adult P. ornatus were chiefly harvested in Northern Samar and Southern Leyte. The other lobster species were either occasional or rare in some areas. Calmer waters and good weather during dry months in Eastern Visayas allow fishers to sail and gather lobsters. The surge in the abundance of P. ornatus and P. penicillatus from July to December was also affected by market demand. Panulirus femoristriga, P. versicolor, and P. longipes subspecies generally peaked from April to June in Eastern Samar and July to September in Northern Samar and Southern Leyte areas. These species would decline in abundance towards the end of the year. The general size structure of spiny lobster catches in Eastern Visayas revealed extreme harvesting of juveniles and sub-adults (< 77.5 mm CL), except for P. ornatus. The fishery could be on the verge of growth overfishing since 50-90% of the catch have CL below their size at first maturity. Panulirus ornatus is targeted at larger sizes (96–107 mm CL) and as a live catch due to its high value and marketability. Raising awareness of the species, reinforcing existing regulations on minimum size limits, and prohibiting the use of compressor diving as a hazardous collection method should be prioritized by fishery managers to protect both the spiny lobster resource and the gatherers in Eastern Visayas.