Preliminary trials on the effects of weaning and larval diets on survival and growth of silver therapon (Leiopotherapon plumbeus) larvae

Abstract only.Success in larval rearing of silver therapon can be achieved through early weaning of fish larvae from live food to artificial diet. Two experiments were carried out to investigate the effects of (a) weaning age (abrupt and gradual) and (b) larval diets (artificial and live foods) on survival and growth of silver therapon (Leiopotherapon plumbeus). In the first experiment, larvae were randomly stocked in round 4-l plastic basins at 15 larvae per basin to provide triplicates of four weaning age treatments (8, 14, 20 and 26 days after hatching or DAH, respectively). Larvae were fed thrice daily for 21 days with commercial feed (CF) and with copepods (COP) which served as the control. Larvae weaned at 26 DAH had the highest survival, body weight and total length among the treatment groups, which were comparable with that of the control. In the co-feeding protocol, larvae were fed Artemia nauplii (ART) as the control group and co-fed with either zooplankton i.e. 50% COP + 50% CF or 50% ART + 50% CF for 8 (8-15 DAH), 6 (14-19 DAH) and 4 (20-23 DAH) days, and suddenly weaned to FM until 21 days. Survival ranged from 22.2 ± 16.8 to 40.0 ± 24.0% between treatments, but was still lower than the control (88.9 ± 3.8%). Body weight and total length were significantly higher in larvae with co-feeding for 4 days (70.1 ± 2.8 mg; 18.1 ± 0.8 mm), but were still lower than that of the control (142.8 ± 7.6 mg; 22.3 ± 0.3 mm). In the second experiment, 26-day old larvae were stocked in 20-l glass aquaria at 4 larvae l-1. Larval diets ((I) commercial prawn feed (38% crude protein); (II) Artemia nauplii; (III) copepods; and (IV) free-living nematode Panagrellus redivivus) were given twice daily for 28 days. Survival was highest in larvae fed Artemia nauplii and poor in copepod fed larvae. Final total length (TL) of larvae fed prawn diet was higher than those fed copepod or nematodes. However, best growth was noted in larvae fed Artemia nauplii (TL= 24.30 ± 0.81 mm; BW = 156 ± 8 mg; specific growth rate or SGR = 5.33 ± 0.19%/d)

Larval rearing of silver therapon (Leiopotherapon plumbeus) in outdoor tanks

Abstract only.Silver therapon (Leiopotherapon plumbeus, Kner 1864), locally known as ayungin, is an important freshwater food fish species found in Laguna de Bay, the largest lake in the Philippines. Its market price is twice that of other most sought after freshwater fishes such as tilapia and milkfish. However, intense fishing pressure on the species has significantly reduced the wild stock in Laguna de Bay. Studies to develop hatchery techniques for this indigenous freshwater fish species are therefore needed to produce seedstock for possible culture and wild stock rehabilitation. This study highlights the successful larval rearing of silver therapon in outdoor concrete tanks. Larvae reared in outdoor tanks with natural food (grown two weeks beforehand) reached the juvenile stage (40 days after hatching (DAH)), suggesting the presence of some suitable live food organisms in pre-conditioned rearing water. However, larval survival rates were low (11.58 ± 6.56% at stocking density of 0.9 larvae l-1), which is probably linked to the density of food items, particularly during the onset of exogenous feeding or due to high stocking density of larvae. To improve the availability of natural food for the larvae, fertilization of the rearing water in the outdoor tanks stocked with larvae at two densities (0.4 and 0.6 larvae l-1) was performed. Larval growth and survival were improved at stocking density of 0.4 larvae l-1 than at 0.6 larvae l-1. Diet composition of first-feeding silver therapon larvae in outdoor tanks inoculated with cultured microalgae (Chorella sorokiniana) and zooplankton was also determined. Larvae were able to consume rotifers and some phytoplankton beginning at 2 DAH and larger preys such as cladocerans and insect larvae starting at 12 DAH. The efficacy of raising silver therapon larvae in outdoor tanks using ambient lake water was also evaluated. Larvae reared in ambient lake water grew well but survival (48.44 ± 7.85%) was significantly improved in treatments where tropical almond or talisay Terminalia catappa leaves were added during the first two weeks of larval rearing

Improved survival and growth of silver therapon Leiopotherapon plumbeus early juveniles through co‐feeding with Artemia and commercial feeds

This study examined the effects of co-feeding Artemia and commercial feeds on survival, growth and fatty acid composition of silver therapon Leiopotherapon plumbeus early juveniles. Triplicate groups of 36 days post hatch (DPH) early juveniles (17.09 ± 1.69 mm; 0.07 ± 0.02 g) were stocked in nine glass aquaria at 25 individuals per aquarium and reared for 60 days on three feeding regimes: (A) Artemia + powdered commercial tilapia feed (35% crude protein (CP)); (B) Artemia + powdered commercial prawn feed (38% CP); and (C) Artemia nauplii only as the control group. Early juveniles co-fed Artemia and commercial feeds had significantly higher survival (97%) than those fed Artemia alone (86%). Except for the condition factors that were similar to the control group, higher mean total length (30.2 ± 1.3 mm and 27.6 ± 1.2 mm), body weight (401 ± 64 mg and 339 ± 46 mg), length- (SGRL; 0.95 ± 0.07%/day and 0.80 ± 0.07%/day) and weight-specific growth rates (SGRW; 2.85 ± 0.27%/day and 2.58 ± 0.22%/day) were also observed in the co-feeding groups, independent of protein, fat and other nutrient levels in commercial feeds. Higher levels of long-chain polyunsaturated fatty acids were reflected in early juveniles co-fed Artemia and commercial feeds than those fed exclusively on Artemia contributing, in part, to the higher growth and survival observed in the co-feeding groups. Together, these results suggest that co-feeding strategy showed best results in terms of growth and survival, and that commercial feed with 35% protein and 6% crude fat levels may be beneficial in supplementing live feed with essential nutrients to optimize production of silver therapon fry during nursery culture.This study was funded by the SEAFDEC Aquaculture Department (Nr-01-F2013B) and the Natural Sciences Research Institute of the University of the Philippines (Diliman) (BIO-16-1-07)

Effects of weaning on survival and growth of silver therapon (Leiopotherapon plumbeus) larvae fed live and artificial diet

This study examined the effects of early weaning strategies on growth and survival of the silver therapon Leiopotherapon plumbeus larvae. In Trial 1, four larval age groups (8, 14, 20 and 26 days post‐hatch (dph)) were abruptly weaned to commercial powdered tilapia diet and compared with wild copepod‐fed group as the control. In Trial 2, another batch of three weaning age groups were subjected to gradual weaning (8 dph larvae with 8 days co‐feeding, 14 dph larvae with 6 days co‐feeding and 20 dph larvae with 4 days co‐feeding) with Artemia nauplii prior to weaning on commercial powdered prawn diet and compared with a control group consisted of larvae fed exclusively on Artemia nauplii. Both weaning trials were conducted for 21 days. A gradual weaning strategy promoted better survival (22.2%–40.0%) among weaning age groups than the abrupt weaning strategy (2.2%–36.7%). Except for those weaned at 26 dph, abrupt weaning resulted in significantly poor growth and survival among all weaning age groups compared with the wild copepod‐fed control group. The highest survival and growth were observed in 20 dph larvae with 4 days live food co‐feeding, although the values were significantly lower than the Artemia‐fed control group. These results suggest that abrupt weaning at 26 dph, and gradual weaning for 4 days from 20 dph promote successful rearing of silver therapon larvae and that a microparticulate diet specifically formulated for this species needs to be developed.The study was conducted with funding support from SEAFDEC Aquaculture Department (Study code: Nr-01-F2013B)

Rearing silver therapon Leiopotherapon plumbeus (Teleostei: Terapontidae) larvae using euryhaline rotifers as starter food

The silver therapon Leiopotherapon plumbeus is an important but dwindling freshwater food commodity in Philippine freshwater habitats. The influence of feeding regimes on growth performance and survival of first-feeding silver therapon larvae fed euryhaline rotifers (Brachionus rotundiformis and B. plicatilis) as starter food was examined. Larvae at 2 days post-hatch (DPH) (1.93 ± 0.07 mm; 200 larvae/basin) were initially reared on rotifers for 12 days followed by Artemia nauplii from 14 to 35 DPH as follows: (A) B. rotundiformis from 2-13 DPH; (B) B. rotundiformis from 2-7 DPH and Moina micrura from 8-13 DPH; and (C) B. plicatilis from 2-13 DPH. After 35 days of rearing, mean survival rates were significantly higher in larvae fed B. rotundiformis (69.2%) than those co-fed B. rotundiformis and M. micrura (34.6%) or B. plicatilis alone (26.3%). Higher ingestion rates were observed for B. rotundiformis-fed larvae (1.6 ± 0.5 to 4.4 ± 0.5 ind larvae-1) than larvae fed B. plicatilis (0.0 to 3.2 ± 0.8 ind larvae-1) during the critical initial feeding stage. However, larvae fed B. plicatilis (20.75 ± 0.48 mm) were significantly longer than those fed B. rotundiformis alone (15.62 ± 0.40 mm) or co-fed B. rotundiformis and M. micrura (18.57 ± 0.58 mm). The fastest growth was observed in larvae fed B. plicatilis, with length increment (LI) and specific growth rate (SGR) of 18.8 mm and 6.8% day-1, respectively. Eye diameter, head length, snout length and pre-anal length increased but were not affected when larvae were fed two rotifer species. These results demonstrate that feeding euryhaline rotifer B. rotundiformis from 2 to 13 DPH followed by Artemia is a suitable feeding regime for better survival of silver therapon larvae under laboratory rearing conditions

Embryonic and larval development of hatchery-reared silver therapon Leiopotherapon plumbeus (Perciformes: Terapontidae)

The embryonic and larval development of hatchery-reared silver therapon Leiopotherapon plumbeus are described to provide essential information on the early life history of this species. Egg size, larval size at hatching, yolk resorption rate, onset of feeding and development of some morphological characters were examined. Fertilized eggs (430–610 µm in diameter) were spherical, yellowish, demersal and slightly adhesive. First cleavage occurred 6 min post-fertilization and embryos hatched 21–24 h post-fertilization under ambient temperature of 27.5 ± 0.1 °C. Newly hatched larvae [1.79 ± 0.04 mm in total length (TL)] with yolk volume of 0.579 ± 0.126 mm3 had no functional or pigmented eyes, mouth or digestive tract. The eyes became fully pigmented and mouth opened [31 and 36.5 hours post-hatching (hph)] shortly before yolk resorption at 39 hph and when larvae had grown to 2.65 ± 0.14 mm in TL. Some morphological characters such as total length, pre-anal length and eye diameter decreased following yolk resorption, which also coincided with the development of foraging capacities shortly before exogenous feeding was initiated. L. plumbeus larvae initiated exogenous feeding at 54 hph, indicating a short (15 h after yolk resorption) transitional feeding period. Larval growth at the early stages of development (54–72 hph) was rapid and steadily increased from 288 to 720 hph, when larvae, 12.05 ± 4.02 mm in TL, closely resembled the external characteristics of their adult conspecifics.The study was funded by the SEAFDEC Aquaculture Department (Study Codes Nr-04-F2010B and Nr-01-F2013B) and UP Natural Sciences Research Institute (Project Codes BIO-09-2-06 and BIO-13-2-04). Part of this work was conducted at the Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan, with support from the Japan Society for the Promotion of Science through its ‘‘Invitation for East Asian Young Researchers’’ Program. Comments of the four anonymous reviewers improved an earlier version of this manuscript. The authors are grateful to MN Santos, MN Corpuz and NB Olorvida for assistance during the experiment

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