Joebert D. Toledo

Preliminary investigation of feeding performance of larvae of early red-spotted grouper, Epinephelus coioides, reared with mixed zooplankton.

Larvae of red-spotted grouper, Epinephelus coioides, were reared inoutdoor tanks with nauplii of copepods (mainly Pseudodiaptomus annandaleiand Acartia tsuensis) and/or rotifers, Brachionus rotundiformis. Grouperlarvae successfully started feeding on early stage nauplii even though theirabundance was as low as approximately 100 individuals l−1 andshowed better survival and growth thereafter compared to those fed withrotifers only. Incidence of feeding reached 100% on day 4 whennauplii were available and only on day 9 when rotifers were given alone.Larvae seemed to be poor feeders at the onset of feeding, attempting tocapture any food organisms in the tank water. Selective feeding ability oflarvae started from day 4 and the larvae then preferred to feed on medium-and large-size nauplii rather than on rotifers as they grew. Larvae appearedto have a better chance at surviving in the presence of early stage nauplii,which were probably caught more easily than rotifers.

Density dependent growth of the tropical abalone Haliotis asinina in cage culture

Abstract The effects of different stocking densities on the growth, feed conversion ratio and survival of two size groups of the tropical abalone Haliotis asinina were determined. Three culture trials were conducted in net cages installed in a sheltered cove, Guimaras Province, Philippines. Trials 1 and 2 were conducted using 15–20 mm abalone juveniles for 150 days, while trial 3 was conducted using 35–40 mm abalone for 180 days. The animals were fed sufficient amounts of the red alga, Gracilariopsis bailinae (= G . heteroclada ), throughout the experiment. There was an inverse relationship between growth (length and weight) and stocking density. Feed conversion ratio was not influenced by density, but was observed to be higher for larger animals. Survival was not significantly affected by density. Net cages are appropriate for culture of H . asinina . This study showed that H . asinina can reach commercial size of about 60 mm in one year. It also showed that growth of H . asinina can be sustained on a single-species diet. An economic analysis will be important in choosing the best stocking density for commercial production.

Marine leech (Zeylanicobdella arugamensis) infestation in cultured orange-spotted grouper, Epinephelus coioides

Heavy infestation of a marine leech occurred among tank-reared juvenile and adult orange-spotted grouper, Epinephelus coioides Hamilton, at SEAFDEC AQD, Philippines with a prevalence of 83% and 17%, respectively. The leeches were attached in large numbers on the fins, lower jaw, under the operculum, eyes, and inside the mouth of the fish. The attachment and feeding sites exhibited frayed fins, hemorrhages and swelling of the hosts skin. External and internal features indicate that the leech is Zeylanicobdella arugamensis De Silva (Hirudinea, Piscicolidae). The parasite can be effectively controlled using 50 ppm formalin bath treatment for 1 h.

Successive spawning of grouper, Epinephelus suillus (Valenciennes), in a tank and a floating net cage

Abstract Wild Epinephelus suillus (Valenciennes) were collected in 1989 to early 1990. To monitor natural spawning in captivity, 6 mature females (3.5–5.0 kg) and 4 mature males (7–12 kg) were transferred to a 4.6×4.6×2 m concrete tank, and one mature female (5.3 kg) was paired with two spermiating males (6.0–6.5 kg) in a 4×4×3 m floating net cage. Spontaneous spawning occurred successively 5–17 times a month from July 1990 to June 1991 (except in May) in the tank and 5–10 times a month from July to October 1990 in the floating net cage. The number of eggs collected, mean fertilization rate and mean hatching rate in the tank and the floating net cage each month ranged from 0.5–15.8 million and 2.3–3.9 million, 67–88% and 72–89%, and 2–81% and 29–68%, respectively. The onset of the monthly spawning cycle in both holding systems was observed over a period of 3 days either before or after the last quarter moon. The results indicate that a minimum number of E. suillus broodstock are required for a year-round supply of fertilized eggs.

Cryopreservation of the euryhaline rotifer Brachionus plicatilis embryos

Abstract A method for the separation and cryopreservation of Brachionus plicatilis embryos is described. Juveniles with uniform development were collected from a cultured stock by passing them through a series of nets. Collected juveniles were cultured and the embryos separated by vigorous vortex mixing as soon as the majority had laid their first eggs. Separated embryos at stage I (cleavage stage), stage II (invagination stage), stage III (symmetrical embryo stage), or stage IV (“eyed” stage) were frozen to −196°C using various concentrations of DMSO and a two-step freezing procedure. No stage I embryos survived freezing and the highest post-thaw survival was obtained with stage III embryos. A DMSO concentration of 10% of the freezing medium resulted in high post-thaw survival while concentrations higher than 10% appeared to be harmful to embryos. Prolonged incubation in 10% DMSO for up to 30 min before freezing increased post-thaw survival. Incorporating the above results, stage III embryos from a single batch culture were incubated in 10% DMSO for 30 min and frozen to −196°C. Post-thaw survival rates of 63%, 62%, 53%, and 55% were obtained after 3, 7, 15, and 30 days of storage in liquid nitrogen, respectively. Survivors fed actively on marine chlorella and started to lay eggs 2–3 days after thawing.

The financial feasibility of small‐scale grouper aquaculture in the Philippines

Abstract This paper presents the results of an economic analysis of the aquaculture of two species of grouper E. coloides (orange‐spotted grouper, green grouper, red‐spotted grouper) and E. malabaricus (malabar grouper, black‐spotted grouper) for small producers in the Philippines. The findings of the analysis indicate that, based on the assumptions, grouper culture is financially feasible. However, the capital requirements for the broodstock, hatchery/nursery, and integrated system may be beyond the financial means of many small producers. These stages of grouper culture may need to be developed as a larger project by private investors or government. The capital investment requirement for grow‐out (not including purchase of transport boxes) is within the financial means of small producers. Loans or other incentives will need to be made available for the small producer, but the cash flow indicates that these loans can be repaid in the first year of production.

Critical factors influencing survival and hatching of milkfish (Chanos chanos Forsskal) eggs during simulated transport

Abstract The effects of loading density, length of transit time, temperature and salinity on milkfish ( Chanos chanos Forsskal) eggs during simulated transport were examined. Rocking motion approximating conditions of transport of eggs collected from milkfish broodstock floating net cages to a hatchery was simulated using a laboratory orbit shaker. Loading densities of more than 7000 eggs/l in shipping bags resulted in decreased rates of survival and correspondingly lower hatching rates. Prolonged shaking simulating extended periods of egg transport also resulted in low egg survival and hatching rates compared to fertilized eggs not subjected to simulated transport. Egg survival after simulated transport at 20°C was lower than at 28°C, except at 20 ppt salinity, where survival was equal. Egg survival at 20°C progressively increased with declining salinity levels whereas high egg survival rates were observed after 2 h of simulated egg transport at 28°C and at the three salinities tested. Hatching rates of fertilized eggs after simulated transport were higher at 28°C than at 20°C regardless of salinity. Neither salinity nor its interaction with temperature affected hatching rates of eggs after simulated transport. These results indicate that survival and hatching of fertilized milkfish eggs after simulated transport is influenced by loading density, transport time, temperature and, to some degree, the salinity of the water. Based on these results, guidelines for handling and transporting milkfish eggs are given.