World Aquaculture 23 eggs were washed thoroughly fresh seawater and placed in a graduated cylinder for separation of buoyant fertilized eggs from those that sank and to obtain volumetric estimates. To remove the settling unfertilized eggs, the bottom water of the spawning tank bottom water was drained daily after the second egg collection in the afternoon and replaced with new seawater. The good fertilized (buoyant) eggs were incubated in cylindrical 400 μm hatching nets (0.7 m dia. x 0.65 m height). The nets were suspended in indoor 5-t rectangular fiberglass tanks with flowthrough filtered and sterilized seawater and all nets were provided with moderate aeration. The eggs were stocked at an average rate of 300 mL/net (approximately 600,000 eggs/ net). Dead eggs were siphoned out from the bottom of the net. The total number of eggs collected from 10 females during the spawning season (4 April-16 May) was 6.42 million or an average of 435,000 eggs/kilogram of female. The total number of eggs produced decreased from 2.76 million during the first two weeks of April to 300,000 during the last two weeks of May. Buoyant eggs amounted to 81 percent of the total. The eggs hatched within an average of 18.5 hrs at an average minimum water temperature of 26.9ºC. The average hatching rate was 42.9 percent of the total incubated eggs and the total number of larvae produced was 2.15 million. Larval Rearing Immediately after hatching the larvae, averaging 1.7-2.0 mm, were collected from the hatching nets by siphoning into 100 μm collection buckets and then transferred to the 5-t indoor fiberglass rearing tanks (LRTs) at a stocking density of 50 larvae/L. The LRTs were supplied with filtered/ sterilized seawater and continuous aeration. At day 1 after hatching, Nannochloropsis algae concentrate2 was initially added to the LRTs at a concentration of 680,000 cells/mL to precondition the water in the tanks, to serve as rotifer food and to stimulate the digestive processes of the fish larvae (Reitan et al. 1997). The microalgae were added continuously until day 20 post-hatch at a density of 300,000 cells/day. From day 2 to 20 days post-hatch, enriched rotifers were provided at a density of 10/mL and from day 21 to 30 post-hatch, at a density of five unenriched rotifers/mL. The rotifer density was monitored twice a day and adjusted to maintain the required density. The S-type rotifers, Brachionus plicatilis, (93.1-106.4 μm), were first grown on yeast (0.5-0.75 g/million individuals) and Chaetoceros and then harvested and placed in the enrichment tanks. Enrichment was done for 48 hrs; in the first 24 hrs, the rotifers were enriched with Packboost, 6 percent EPA, 8 percent DHA3 and in the second 24 hrs with HUFA, ≥ 30 percent ω3 fatty acids, ≥ 12 percent EPA, ≥ 12 percent DHA, and ≥ 1.75 percent ARA4. Enriched Artemia nauplii3 were offered from day 14 to 20 post-hatch at a rate of 0.05-0.1 nauplii/mL. Unenriched Artemia nauplii were provided from day 21 to day 30. Enrichment of Artemia was done with 300 ppm Packboost 3 hrs before feeding to the larvae. From day 4 to 20 surface skimmers were introduced in the LRTs. The skimmers were cleaned every six hours using soft paper sheets. On day 11, the first prepared feed of <200 μm (Progression) was distributed hourly in quantities of 2-5 g. On day 15, prepared feed of 200-300 μm (Proton, INVE, Belgium) was introduced and on day 20, feed of 360-560 μm5 was provided. On day 25 distribution of the smallest size feed was terminated and only feeds of latter two sizes were provided until the end of the 30day rearing period. The water exchange rate in the LRTs was dependent on feeding protocol. During the period of enriched rotifer feeding the water was replaced on days 8-13 at a rate of 10-20 percent daily. Beginning on day 14 when enriched Artemia were added, the daily Table 1. Spawning and hatching performance of spangled emperor during 4 April -16 May 2005. Spawning Period 4 April–15 April 16 April-30 May 1 May-15 May 16 May-29 May Lunar cycle 2nd 1st 2nd 1st Water Temp.(°C) Minimum 24 26 27.5 30 Maximum 25 27 28 31 Salinity (‰) 52 52 52 52 Collected eggs (x106) Total 2.76 2.44 0.92 0.30 Buoyant 1.80 2.36 0.76 0.28 Sinking 0.96 0.08 0.16 0.02 Incubation period (hrs) 20.0 17.5 17.5 19.0 No. larvae (x106) 0.125 1.411 0.507 0.107 Hatching rate (percent) 6.95 59.78 66.71 38.21
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