Eduard M. Rodriguez

Pen culture of mud crab Scylla serrata in tidal flats reforested with mangrove trees

Abstract Growth and survival of mixed sex mud crabs Scylla serrata (Forskal), held in 200 m 2 pens located in reforested mangrove tidal flats, were evaluated. The effects of stocking density (0.5 or 1.5 m −2 ) and feed (salted fish bycatch or a mixed diet of 75% salted brown mussel flesh and 25% salted fish bycatch) were determined in a replicated factorial experiment. Duration of the experiment was 160 days. There were no significant differences ( P >0.05) in growth, apparent feed conversion ratio (FCR), survival, and production among the two types of feed. Regardless of feed, the mean±SE FCR of 5.30±0.34 and survival of 56.00±1.90% at 0.5 m −2 stocking density were significantly better ( P 0.05) than at 1.5 m −2 stocking density (7.6±0.63 FCR and 33.00±3.61% survival). However, growth was not significantly affected by stocking density. Cost–return analysis on a per crop per 200 m 2 basis showed that the use of either of the two stocking densities with either diet was economically viable with a return on capital investment of 49–68%. However, crabs stocked at 1.5 m −2 and fed a mixed diet of 75% salted brown mussel flesh and 25% salted fish bycatch is more profitable. The integration of crab aquaculture within natural mangroves is therefore feasible in the Philippines, providing both immediate and long-term commercial and environmental benefits.

Culture and economics of wild grouper (Epinephelus coioides) using three feed types in ponds

Abstract The performance of wild Epinephelus coioides juveniles was compared by feeding with live tilapia juveniles, fish by-catch, and formulated diet for 5 months in grow-out ponds. To minimize cannibalism, the groupers were graded into small (BW=24.9±7.3 g), medium (45.8±5.7 g), and large (84.1±30.0 g) size groups as block in a Randomized Complete Block Design (RCBD) and reared in nine 350-m2 ponds. To supply the tilapia juveniles, adult tilapia were grown 2 months prior to stocking of grouper at a rate of 15 tilapia/grouper. Grouper fed by-catch were significantly higher (P 400 g and only 14% was classified

Evaluation of hatchery-based enhancement of the mud crab, Scylla spp., fisheries in mangroves: comparison of species and release strategies

Ranching, stock enhancement and restocking are management approaches involving the release of wild or hatchery-bred organisms to enhance, conserve or restore fisheries. The present study, conducted from April 2002 to November 2005, evaluated the effectiveness of releasing wild and hatchery-reared (HR) mud crabs in the mangroves of Ibajay, Aklan, Philippines where preliminary studies demonstrated declining fishery yields, abundance and size of crabs. Comparison of survival and growth of wild-released and HR Scylla olivacea and HR Scylla serrata demonstrated the effect of nursery conditioning, size-at-release and species differences. Overall yield and catch per unit effort (CPUE) increased by 46% after stock enhancement trials. Recapture rates of released crabs were highest in wild-released S. olivacea and in crabs measuring 65.0–69.9 mm carapace width (CW) and lowest in non-conditioned HR S. serrata. Growth rates were highest for conditioned HR S. olivacea and lowest for conditioned HR S. serrata (11.7 and 3.7 mm month–1 respectively). Fishing mortality was highest for S. olivacea, whereas natural mortality was greater for S. serrata. Conditioning hatchery-bred animals before release is also important in obtaining higher survival. S. olivacea was the more appropriate of the two species for release in mangrove habitats inundated with low-salinity water. However, there is a need for site-specific studies to evaluate the effectiveness of releases.

Nursery rearing of Penaeus monodon (Fabricius) using suspended (hapa) net enclosures installed in a pond

Abstract The use of suspended (hapa) nets as nursery enclosures for shrimp fry was tested. In the first trial, four stocking densities (72, 144, 288, and 432 fry m−3) of P. monodon fry (PL20, body weight = 8 mg, body length = 12.6 mm) were evaluated in 1×1×1.5 m hapa nets. Results showed that shrimp BW, BL, and survival rates were inversely related to stocking density. Shrimp fry stocked at 72 fry m−3 attained significantly greater BL of 22 and 37 mm and BW of 50 and 260 mg after 15 and 30 days, respectively, and survival of 92%. A verification trial using PL28 (BW = 10 mg, BL = 13.2 mm) at a stocking density of 288 fry m−3 in hapa nets of 2×3×1.5 m yielded a mean survival of 97%, BL 48.1 mm, and BW 780 mg. Hapa nets are therefore useful as alternative shrimp fry nursery systems in the absence of specialized tanks or pond nursery facilities.

Semi-mass culture of the dinoflagellate Gymnodinium splendens as a live food source for the initial feeding of marine finfish larvae

A technique was developed for the semi-mass culture ofthe unarmored dinoflagellate, Gymnodiniumsplendens under laboratory conditions. A maximumcell density of 4600 to 6800 cells ml−1 was observedwithin 8 to 11 days of culture. An initial feedingtest for 8 days with three important marine finfishlarvae showed that red spotted grouper, Epinephelus akaara preferred G. splendensfed 200 cells ml−1 with 44% survival. The Japanesestripe knife jaw, Oplegnathus fasciatus,attained 22% survival fed a combination of G. splendensand rotifers (200 cells ml−1 and 5ind. ml−1, respectively). Red sea bream, Pagrusmajor larvae did not respond well to the initialfeeding of G. splendens alone. Red seabream were observed to be solely dependent on rotifers(5 ind. ml−1) as initial food. Gymnodiniumsplendens may be used as a live food in the initialfeeding of red spotted grouper larvae (E. akaara) toreduce mortality and to further enhancegrowth during the critical first few days ofrearing.