Marietta N. Duray

The effect of background color and rotifer density on rotifer intake, growth and survival of the grouper (Epinephelus suillus) larvae

Abstract Rotifer intake and early growth and survival of Epinephelus suillus larvae were determined in terms of rotifer visibility against the background color of rearing tanks and density. The larvae were stocked at 30 l −1 in 200-l fiberglass tanks with phytoplankton (green water). Larvae were fed rotifers at densities of 5, 10 and 20 ml −1 . Growth and survival were comparable among larvae in both tan and black tanks with green water. Rotifer intake was significantly higher in larvae in tan tanks. In black tanks, the survival of larvae at Day 14 was enhanced by the high rotifer density of 20 ml −1 . Rotifer intake and growth of larvae were similar at all densities.

Improved larval survival at metamorphosis of Asian seabass (Lates calcarifer) using ω3-HUFA-enriched live food

Abstract Asian seabass (Lates calcarifer) larvae were fed Brachionus cultured on Chlorella and, as soon as ingestin was possible, different types of Artemia, i.e., nauplii of the San Francisco Bay (SFB) strain, Great Salt Lake (GSL) strain or GSL nauplii that had been bioencapsulated with an emulsion containing high levels of the ω3-HUFAs (highly unsaturated fatty acids) 20:5 and 22:6. San Francisco Bay Artemia with a good natural fatty acid profile and small body size could be offered earlier than the larger but HUFA-poor Great Salt Lake strain. The poor nutritional quality of the latter, however, could be corrected by enriching the nauplii with an ω3-HUFA emulsion for 24 h, after which time high levels of the ω3-HUFAs 20:5 and 22:6 were obtained. When the Artemia diet offered before metamorphosis included natural or supplemented essential fatty acids, no significant differences in dry weight, length or survival of the fish were noticed, as compared to fish fed the naturally deficient GSL Artemia. Onset of metamorphosis and physiological condition after metamorphosis, however, were influenced by the HUFA content of the ingested prey. Seabass larvae fed SFB or enriched GSL Artemia started metamorphosis on day 19, while those in the non-enriched series never achieved metamorphosis and died of a nutritional deficiency syndrome by day 27. An indication of the physiological condition of the larvae and the early detection of the syndrome was possible by subjecting 21- and 25-day-old larvae to a stress test: abrupt exposure of the larvae to 65-ppt saline water resulted in abundant and early mortality in HUFA-deficient fish larvae. Fry receiving ω3-HUFA-fortified Artemia had a superior physiological condition which was reflected by significantly lower mortality figures in the stress test.

Effects of continuous lighting on growth and survival of first-feeding larval rabbitfish, Siganus guttatus☆

The effects of 24-h lighting on feeding, growth and survival of first-feeding larvae of Siganus guttatus were tested. Continuous light gave a higher mean survival (31.69%) with a maximum of 40.50% compared to natural daylight (17.10%). Larval size on day 7 also showed that continuous lighting gave improved results. Although feeding incidence increased with age of the larvae, a higher incident rate was observed for larvae held in continuous light from day 3.

Larval rearing of the grouper Epinephelus suillus under laboratory conditions

Abstract A protocol for rearing orange-spotted rockcod, Epinephelus suillus in the hatchery is described. The feeding regime consisted of Chlorella, Brachionus, Artemia and minced fish. With this regime, survival rates at Day 24 were 19.8% in 3-ton tanks and only 7.4% in 0.5-ton tanks. From an initial length of 1.62 mm on Day 0, larvae grew to 10.94 mm on Day 24 and 51.4–65.1 mm on Day 60. Larval growth and survival rate were improved when larvae were fed screened (less than 90 μm) Brachionus during the first 2 weeks. Survival was even better among larvae fed Brachionus until Day 35. Artemia, at a density of 3 ml−1, given once daily to larvae in 24 ppt seawater improved growth and survival.

Effects of DHA-enriched live food on growth, survival and incidence of opercular deformities in milkfish (Chanos chanos)

Abstract The use of commercial enrichers to improve the nutritional quality of live food in larviculture of milkfish was investigated. Fish were either fed rotifers cultured on Chlorella sp. and newly hatched Artemia nauplii (Control, Trt I) or rotifers and Artemia given DHA enrichment diets (DHA-treated, Trt II). Results showed survival was significantly better (P 0.05) between the control and DHA-treated fish during the hatchery phase, extensive rearing of the postlarvae (fry) in nursery ponds for another 60 days showed that DHA-treated fish exhibited significantly better (P 0.05). The lack of a viable and reliable method of mass culturing copepods as live food in the hatchery makes the use of off-the-shelf commercial enrichment diets for rotifers and Artemia a practical option in the larval culture of milkfish.

Year-round spawning and seed production of the rabbitfish, Siganus guttatus

Abstract A series of experiments on the spawning and larval rearing of Siganus guttatus was conducted during a 14-month period in 1984–1985. Spawning occurred every month throughout the year, without hormonal treatment, between the first quarter and the full moon. Fertilization rates and hatching rates were high, with means of 84.2% (n=38) and 89.6% (n=34), respectively. Females that had been fed diets rich in cod liver oil or in a cod liver oil/soybean oil/soybean lecithin mixture spawned repeatedly for at least 4 consecutive months. Larvae reared in 20, 26, and 32‰ salinities showed no significant differences in survival rates at day 21. Survival was higher for larvae fed during days 2–4 with rotifers strained through an 80-μm-mesh plankton net than for those fed unstrained rotifers. Larvae readily accepted Artemia nauplii and artificial diets when these were first introduced on day 15 and day 23, respectively. Higher larval survival was obtained in large tanks (≥5 m3) than in small tanks (500 l). Survival rates of 3.5–16.6% ( x =7.5% ) at day 45 were obtained in six trials of mass larval rearing and 5500–50100 ( x =27 700 ) juveniles per female were produced at day 45, ready for stocking in grow-out farms.

Breeding and larval rearing of the rabbitfish, Siganus guttatus (Bloch)

Abstract Females of Siganus guttatus reared to sexual maturity in canvas tanks were induced to spawn by using human chorionic gonadotropin (HCG, Ayerst) at 500 IU/fish or about 2 IU/g body weight. The amount of HCG used depended on the initial mean egg diameter; the smaller the diameter, the more HCG was used. Fish with oocytes characterized by germinal vesicle migration (mean egg diameter ≥ 0.47 mm) spawned without HCG injection. Fertilization and hatching rates for both treated and untreated fish were more than 90%. The larvae were reared to metamorphosis using rotifers from day 2–17, rotifers + newly hatched Artemia nauplii from day 18–20 and rotifers + newly hatched Artemia nauplii + artificial feed from day 21–35. In addition, Isochrysis galbana was introduced to the rearing tanks from day 1–10 and Chlorella sp. and/or Tetraselmis sp. from day 1–35. Survival rates of larvae tended to be lower as the broodstock became older.

Induced breeding and larval rearing experiments with milkfish Chanos chanos (Forskal) in the Philippines

Abstract Salmon pituitary homogenate was used alone or in combination with human chorionic gonadotropin, to induce spawing in captive and wild adult milkfish at ambient temperature (26–30°C) and salinity of 34%.. Healthy or slightly injured females having oocytes with a minimum mean diameter of 0.66 mm could be induced to spawn in captivity using a total dose of 20 mg SPH/kg + 3000 IU HCG/kg given in two injections. Badly injured females did not respond readily to the hormone and required more than two injections to induce ovulation. Milkfish larvae were reared successfully to metamorphosis using only Chlorella -fed rotifers during the first 10 days. Survival rates were greatly improved when, aside from Chlorella and Chlorella -fed rotifers, Isochrysis galbana and Tetraselmis chuii were added to the rearing tanks.

Salinity tolerance of larvae of the mangrove red snapper (Lutjanus argentimaculatus) during ontogeny

Abstract Salinity tolerance and the effects of salinity on growth, condition factor and chloride cell (CC) densities were evaluated for Lutjanus argentimaculatus larvae during ontogeny. Tolerance of L. argentimaculatus larvae to abrupt changes of salinity from 32 ppt varied with age. Periods to 50% mortality (LT 50 ) were significantly ( P L. argentimaculatus larvae, regardless of age (0-, 7-, 14-day-old), showed significantly longer LT 50 when abruptly transferred to 8 and 16 ppt than for transfers to 24 and 40 ppt ( P L. argentimaculatus larvae at 16, 24, 32 (control) and 40 ppt was not significantly different either at the end of the first rearing phase (days 0–21) or second phase of rearing (days 22–50). Survival was significantly lowest at 40 ppt (4.3%) at the end of first phase of rearing ( P K ) of larvae reared at lower salinities was significantly higher than that of fish at 40 ppt ( P

Transport of hatchery-reared and wild grouper larvae, Epinephelus sp.

Abstract Optimum packing conditions for the transport of hatchery-reared and wild grouper larvae were investigated under simulated condition or actual air transport. Simulation of transport motion was done through the use of an electric orbit shaker to identify the best packing conditions for the transport of grouper larvae at various ages. Simulated transport was conducted in hatchery-reared grouper larvae at day 35 (mean TL=14.73 mm), 45 (mean TL=15.23 mm) and 60 (mean TL=28.16 mm) at packing densities of 50, 100 and 200 larvae l −1 and at high (28 °C) or low (23 °C) temperatures. Packing density of 50 larvae l −1 was best for 45- and 60-day-old larvae 8 h transport at low temperature. However, packing density could be increased to a maximum of 100 larvae l −1 8 h transport at 23 °C with mortality rates ranging from 2.3% to 5.3%. The increase in total NH 3 level was dependent on temperature, packing density and size of larvae. High packing density (100–200 larvae l −1 ) and temperature (28 °C) resulted in increased NH 3 level and mortality rates during transport. In addition, regardless of the temperature, NH 3 levels were consistently higher for 60-day-old larvae. Day-60 grouper larvae displayed strong resistance to handling/mechanical stress compared to 35-day-old larvae probably because most are already fully metamorphosed at this stage. Based on these results, a packing density of 50 larvae l −1 , a temperature of 23 °C and larval age of 60 days were considered as the best transport conditions for hatchery-reared grouper larvae. When these transport conditions were used in experiment 2, for 26-day-old hormone-metamorphosed, 60-day-old naturally metamorphosed or 60-day-old pre-metamorphosing hatchery-reared grouper larvae, a 100% survival rate was attained in all treatments. Seven days of hormone (T3) treatment did not accelerate metamorphosis of wild-caught transparent grouper larvae (tinies) significantly. Survival rates of hormone-treated transparent tinies (H-tinies), untreated black tinies (B-tinies) and untreated transparent tinies (T-tinies) were also similar after 8–9 h air transport (experiment 3). The results of the current study suggest that T3 treatment did not affect the performance of hatchery-reared and wild-caught transparent tinies/larvae during transport. In addition, mass mortalities of these transported tinies during the nursery phase were associated with nutritional aspect and the sudden confinement of these undomesticated wild-caught grouper to small space rather than transport or hormone treatment effects.