Optimum stocking density and feeding level for laboratory‐reared early‐stage silver therapon (Leiopotherapon plumbeus) larvae

Growth, survival and feeding of early‐stage silver therapon Leiopotherapon plumbeus larvae reared at different stocking densities and feeding levels were examined. Larvae (8 days post hatch (dph); 0.38–0.50 mg body weight (BW); 5.33–6.90 mm in total length (TL)) were stocked at densities of 5, 15, 25 and 35 larvae/L and co‐fed with live food (Brachionus rotundiformis and Artemia nauplii) and formulated microdiet or fed Artemia alone for 28 days. Another batch of 8 dph silver therapon larvae (0.65 mg BW; 9.47 mm TL) were stocked at 15 larvae/L and were fed 1, 2 or 5 Artemia nauplii/mL for 28 days. Survival at lower densities (5 and 15 larvae/L) was significantly improved than in high‐density reared larvae. Furthermore, larvae fed Artemia alone showed higher survival (20.4%–81.4%) than those offered live food and formulated microdiet combined (3.5%–32.9%) in each stocking density, indicating the suitability of Artemia for early‐stage silver therapon larvae. Growth parameters were significantly affected by stocking density in larvae fed Artemia alone but not in the live food and formulated microdiet co‐fed group. No significant differences in growth and survival were observed in silver therapon larvae reared on three feeding levels. However, higher feed intake at 5 nauplii/mL resulted in significantly higher body lipid contents than those fed 1 or 2 nauplii/mL. The results suggest that larvae held at stocking densities of 5 and 15 larvae/L and fed 5 Artemia nauplii/mL promote maximum growth, survival and higher feed intake of early‐stage silver therapon larvae under laboratory conditions.This study was supported by SEAFDEC Aquaculture Department under the Study Code: Nr-01-F2013B

Effects of exogenous hormones and broodstock age on the spawning response of captive silver therapon Leiopotherapon plumbeus

Evaluation of appropriate hormone and ideal broodstock age for optimal breeding efficiency may ensure the production of good quality eggs and larvae in the hatchery. In this study, the spawning response of captive silver therapon Leiopotherapon plumbeus to various hormonal treatments and broodstock age was examined. In Experiment 1, spawning success, latency period, absolute and relative fecundity, fertilization and hatching rates, and larval production of female silver therapon broodstock were determined after ovulation and spawning in response to human chorionic gonadotropin (hCG; 5000 and 10,000 IU/kg), Ovaprim (0.5 ml/kg), hCG + Ovaprim (5000 IU + 0.5 ml/kg; 10,000 IU + 0.5 ml/kg) or hCG + domperidone (5000 IU + 0.5 ml/kg; 10,000 IU + 0.5 ml/kg). In Experiment 2, reproductive performance of four domesticated broodstock age groups (1+, 2+, 3+ and 4+-year old) was examined for five consecutive months, coinciding with the spawning season. Higher dose of hCG + Ovaprim resulted in higher spawning (100%), fertilization (99.7 ± 0.1%), and hatching (85.8 ± 5.5%) rates than the other treatments. The effect of age on reproductive indices was not significant. However, better spawning performance was observed in 1+ to 3+-year old broodstock, with higher fertilization (96.8–98.5%) and hatching (63.7%–77.2%) rates than among the oldest age group (82.9% and 57.2%). Together, results suggest that the combination of hCG + Ovaprim is highly effective in inducing ovulation and spawning in silver therapon, and that domesticated broodstock up to 4+ years of age could still be used for breeding activities and seed production.This study was supported by the SEAFDEC Aquaculture Department (Br-02-F2015B). The assistance of Mr. N. B. Olorvida in the conduct of the experiment is appreciated

Point-of-no-return and delayed feeding mortalities in first-feeding larvae of the silver therapon Leiopotherapon plumbeus (Kner) (Teleostei: Terapontidae)

This study examined the incidence of mortalities among first-feeding post-yolk sac silver therapon Leiopotherapon plumbeus (Kner) larvae deprived of live food in the hatchery. Starting after their yolk was consumed at 40 h post-hatch (hph) and every 2 h thereafter until 54 hph, larvae were fed and exposed to live food for an hour only and their performance was observed after initial feeding at 25 °C. Feeding incidence progressively increased until 48 hph as larval mouth gape increased during exogenous feeding, but oil globule volume progressively declined until full exhaustion at 52 hph. All starved larvae fed at 48 hph but feeding incidence progressively declined until larvae ceased to feed at 54 hph to coincide with a significant reduction in survivorship, indicating that larvae have reached their point-of-no-return (PNR) at 50 hph despite the availability of food. Delayed initial feeding of un-fed post-yolk sac larvae starting at 46 hph until 54 hph resulted in significantly higher feeding incidence among 46−48 hph larvae than those fed after 50 hph, which did not survive longer than 10 h after initial feeding. These results demonstrate that silver therapon larvae have a very brief transitional or mixed-feeding period of 12 h after yolk exhaustion so that initial feeding beyond 50 hph when larvae have reached their PNR results in early onset of death

Improved survival, prey selectivity and diel feeding cycle of silver therapon Leiopotherapon plumbeus (Perciformes: Terapontidae) larvae reared in tanks with substrate

Physical substrates in the rearing environment can influence the early survival and feeding patterns of captive-reared fish. In this study, we determined whether substrates affect the survival and growth of hatchery-reared silver therapon Leiopotherapon plumbeus larvae as well as examined their prey selectivity and diel feeding cycle. Newly hatched larvae [1.92 mm total length (TL)] were reared for 40 days in triplicate 4 m3 tanks with or without tropical almond Terminalia catappa leaves as substrate. Prey selectivity of larvae reared in tanks with substrate for 35 days from the yolk-sac stage was measured by the Chesson’s selectivity index (αi). Diel feeding cycle of 3-4 days post-hatch (dph) silver therapon larvae reared in tanks exposed to natural light cycle and fed wild zooplankton was also studied. Larvae reared in tanks with substrate had significantly higher survivorship (48.44 ± 7.85%) than those reared in tanks without substrate (26.73 ± 1.60%). However, total length, specific growth rate and body weight of silver therapon larvae from tanks with or without substrate were not significantly different. Silver therapon larvae are generalist predator, demonstrating a degree of prey selectivity in some prey items during early ontogeny. Prey selectivity of silver therapon larvae varied during larval ontogeny, with higher Chesson’s selectivity index for copepod nauplii among the smaller fish larvae (2–5 dph; 2.94–5.17 mm TL), cladocerans (Moina micrura and Bosmina coregoni) among intermediate (6–11 dph; 5.72–9.60 mm TL), and ostracod, cladoceran and insect larvae among larger fish (12–35 dph; 10.28–20.96 mm TL). Larvae showed a diel feeding cycle where they actively fed during daylight hours, with a peak in the late afternoon, and reached a minimum at dark. Together, these findings advance our understanding of the feeding predatory behavior and efficiency of silver therapon larvae and preference for tanks with substrate that improve their survival.This study was funded by the SEAFDEC Aquaculture Department (Project Nos. Nr-01-F2013B and Br-02-F2015B). The authors are grateful to NB Olorvida for his assistance in the conduct of the experiment. Handling of fish specimens complied with existing regulations of the Philippines

Potential use of agricultural wastes in aquafeed production

Disposal of agricultural wastes are posing environmental hazards which leads to efforts of efficiently utilizing them. This study surveyed a sugar central and a fruit processing plant to collect data on the volume of wastes from representative agricultural crops (e.g. mango, citrus, pineapple, sugarcane, papaya and soybean) in the Philippines during the 2012–2013 and 2014–2015 seasons, respectively. Their potential use in aquafeed was examined in terms of nutritional quality, presence of anti-nutritional factors (ANFs) and pesticide residues. About 40 to 60 % of agricultural wastes generated after processing were peels, pulps or brans, seeds, bagasse, molasses and okara. Most of the agricultural wastes had high levels of fiber and carbohydrate, and low levels of protein, although okara (25 % crude protein) and citrus by-products (11–16 % crude protein) showed acceptable nutritional quality. ANFs such as lignin are largely present in all agricultural wastes, whereas high levels of phenols, and saponins and alkaloids were found in mango seeds and mango peels, respectively. Pesticide residues were detected only in mango and citrus peels but at levels below the maximum residue limits of FAO Codex Alimentarius. From both nutritional and environmental perspectives, agricultural wastes have potential use in aquafeed production but their suitability should be further elucidated in diets for omnivorous fish species such as tilapia.The study was supported by the Government of Japan – Trust Fund 6 under the study code: 8300-B-RD-FD0415. The authors thank the staff of the sugar central, fruit processing plant and government offices for sharing their data with the authors and Mr. Nemencio Olorvida for his assistance during field collection