Introduction
Asian Seabass or Barramundi, Lates calcarifer, is one of the 15 species of finfish most produced in the world through aquaculture systems. In the last 20 years, the production of this species showed an increase of 80%, from 18.1 thousand tons in 2000 to 105.8 thousand tons in 2020 (FAO, The State of world fisheries and Aquaculture 2022).
Barramundi aquaculture industries are well-established in Thailand, Malaysia, Singapore,
Indonesia, Hong Kong, Taiwan, the Philippines and Australia.
The feeding regime for larval rearing of Barramundi is similar to other marine species; the green water technique is used in the initial stage of larval development, together with rotifers, followed by co-feeding of Artemia and dry diets (Aquaculture of Asian Seabass or Barramundi, Global Aquaculture Advocate, 2020).
The present study, conducted on a research scale between BRINE research centre (Indonesia) and SFA marine aquaculture centre (Singapore), investigated the application of Natura pRo and ExL in warm water culture conditions in the backyard and advanced production systems.
The effect of rotifer replacement was also investigated by introducing dry feed from the first days of exogenous feeding. Moreover, the importance of live feed enrichment was shown by comparing different feeding regimes.
Materials and methods
Asian Sea bass experiments
Experiment 1: Backyard system (Indonesia)
Hatched Asian Seabass larvae, originating from the same pool of eggs, were stocked at the density of around 15 larvae. l-1 in 4,000l larval rearing tanks. No pure oxygen and no continuous water renewal were used. The water temperature during the larval rearing was 28±1°C.
The effect of dry algae, live feed enrichment and early dry feed introduction was compared to the standard protocol (using fresh algae and not enriched live feed) from 0 to 25dph.
In both treatments, Control (Tr1) and RS (Tr2), algae were used from day 2 to 18ph. Enriched rotifers were fed from day 2 to 12ph in the Experimental treatment (reduced by 50% compared with the Control) and rotifers cultured by fresh algae were fed until 19dph in the Control. In Tr2 AF Artemia was fed from 10 to 13 dph, and enriched Artemia was fed from 13dph to 23dph. While in the Control group, non-enriched Artemia was provided from 13 to 23 dph. Different dry diets were used in the two groups: in the Control, Otohime was used from day 8 onwards and in the RS (Rotifer Substitution) group Natura was used from day 3 onwards.
The trial finished at 25 dph with the first grading.
A natural photoperiod was used (12L/12D), and the treatments were done in triplicate.
During the larval rearing period, from 5dph, biometrics were carried out to compare growth rates, every 5 days. A salinity stress test was done to determine the stress resistance before the grading. At 25dph, growth, survival rate, final fish number per tank, fish size distribution and feed consumption were determined.
Experiment 2: Advanced system (Singapore)
Hatched Asian Sea bass larvae, originating from the same pool of eggs, were stocked at the density of around 30 larvae.l-1 in 4,000l larval rearing tanks under controlled conditions: pure oxygen and continuous water renewal were used. The water temperature during the larval rearing was 30±0.1°C.
The effect of the rotifer substitution and early dry feed introduction was compared to the standard protocol from 0 to 21dph.
In both treatments, Control (Tr1) and RS (Tr2), fresh algae (Nanochloropsis) were used from day 1 to 14ph. Rotifers were enriched in both treatments and were fed from day 2 to 14 dph (Tr2 was fed with 50% less of rotifers compared with Tr1). Artemia AF was fed from day 10 to 14dph, and enriched Artemia was fed from 15dph to 21dph. Different dry diets were used in the two groups: in the Control, Otohime was used from day 14 onwards and in the RS group, Natura was used from day 2 onwards.
The trial finished at 21dph with the first grading.
A photoperiod of 12L/12 D was used, and the treatments were done in duplicate.
During the larval rearing period, from 2dph, biometrics were carried out to compare growth rates, every 5-7 days.
At 21dph, deformity, survival rate, final fish number per tank and feed consumption were determined.
Results
The Asian Seabass larvae reared in a regime of reduced enriched rotifers and early use of dry diets showed similar growth, better performance and survival if compared with a standard feeding protocol. The adaptation of the protocols resulted in 42% rotifers substitution in Singapore and 69% in Indonesia.
Conclusions
This study shows that Asian Sea bass larvae can be reared under a feeding regime with reduced offers of rotifers, obtaining a good survival rate and good fry quality when enrichment for the live feed and balanced diet is used from the first days of exogenous feeding. The importance of live feed enrichment, well known in European aquaculture, is a central theme that must be transmitted in the Asian aquaculture hatcheries.
A high-quality diet is fundamental to obtain optimal growth and quality in the larval rearing of Asian Seabass, showing that Natura pRo and ExL, developed for the European finfish species, demonstrated a high versability in tropical conditions.
References
FAO: The State of world fisheries and Aquaculture, page 43, 2022.
Aquaculture of Asian Seabass or Barramundi, Global Aquaculture Advocate, page 1/5, 2020.