World Aquaculture March 2019

WWW.WA S.ORG • WORLD AQUACULTURE • MARCH 2019 41 ( C O N T I N U E D O N P A G E 4 2 ) how larval rearing trials were previously conducted in Hawaii. They addressed the criticism that aquaculture research in the US at the time was not being done in a scientific manner. This was clearly not the way Japanese researchers were conducting their efforts. Key results from larval rearing experiments were the determination that first feeding was dependent on density rather than size of the live food organisms presented to larvae. The quantitative requirements for both rotifer density in relation to the density of first- feeding larvae of both mullet and milkfish were determined. It was interesting that it was the same for both species: 10-20 rotifers/mL and 10-20 fish larvae/L (Eda et al . 1990a, b). Results were combined and the complete rearing protocol for both species was determined. This also allowed projection of the size of the phytoplankton and rotifer production facilities required for small- and large-scale hatcheries. Dr. Harry Ako focused on the amino acid and fatty acids of the live food organisms that were especially important for marine fish larval survival, development and growth. Particularly important was demonstrating that milkfish larvae were able to synthesize their own essential long-chain fatty acids (Tamaru et al .1993). The result differed fromwhat was reported for other marine species, including striped mullet. The major impact was demonstrating that there was great flexibility in the way rotifers could be grown for first-feeding milkfish larvae. Current methods employed in Indonesia continue to use N. oculata in the culture of the majority of marine fish species, including grouper larvae, allowing for the continued diversification to other species without the use of another phytoplankton species. Milkfish Culture in Bali By 1990 milkfish broodstock located in spawning tanks at the Institute for Mariculture Research and Development (IMRAD) on north Bali were spawning naturally (Table 1). Using an average fecundity of 450,000 eggs per spawn, the average annual production was estimated to be 95.4 million milkfish eggs just from this one facility. The greatest number of spawns occurred fromOctober through December, coinciding with the monsoon season in Indonesia, although milkfish spawned throughout the year at this facility. In 1993 it was estimated that Indonesia required approximately three billion milkfish fry per year to cover all current growout A B TABLE 3. Monthly and annual spawnings at IMRAD. Month 1990 1991 1992 Average Jan 1 20 16 12 Feb 7 9 1 6 Mar 13 32 19 21 Apr 14 19 7 13 May 24 14 16 18 Jun 11 6 8 8 Jul 21 3 2 9 Aug 22 8 18 16 Sep 29 15 15 20 Oct 29 26 35 30 Nov 28 30 21 26 Dec 27 42 30 33 Total 226 224 187 212 LEFT, FIGURE 7. Another backyard milkfish hatchery, Gondol, Bali, Indonesia, 1993. RIGHT, FIGURE 8. Pond being prepared for producing milkfish to be used for bait.