48 MARCH 2026 • WORLD AQUACULTURE • WWW.WAS.ORG The daily water exchange rate was 50% from 2 dph to 5 dph, then increased to 100% from 6 dph to 12 dph. and finally, 200% from 13 dph to 40 dph. Tank bottom siphoning was done regularly from 9 dph until 35 dph. Dissolved oxygen, ammonia, salinity temperature and pH were 4.5 ±0.5 mg/l, 0.2±0.05 mg/l, 35 ±2 ppt, 27±3 °C and 8.5±0.3, respectively. On 40 dph fish in all three tanks were harvested, resulting in 47,800 weaned fry averaging 0.2 gm, attaining 11.7 % survival. Juveniles Development and Growth Collected fry from the larval tanks were immediately transferred to a 15-m3 nursery tank and reared further, for a period of 25 days. The fish were fed with 0.5 to 0.8 mm feed containing 52% crude protein at a rate of 5-8% of their body weight per day. Water quality parameters were carefully maintained, with temperatures ranging from 26 to 32 degrees Celsius, pH levels between 7.3 and 7.8, and dissolved oxygen concentrations between 4.5 to 6.5 mg/l. Weekly samples were collected, and daily feeding rates were adjusted to 8-10%. After 25 days, 40,000 fingerlings (Figure 4) were harvested, averaging 2.5±0.5 grams in body weight, with a feed conversion ratio (FCR) of 0.85. The survival rate during the nursing phase was 83.6%. Upon completion of the nursing period, the fingerlings were harvested and transferred to the grow-out cage farm. Black Spot Snapper Grow-out Trial in the Cage Farm At the time of stocking (5th of July 2024) in the cage farm, the salinity was 42 ppt and water temperature was 33.9˚C. The fish were active and feeding patterns were adjusted with modifications in feed size and quantity. Initially a 1.5-2.0 mm feed size was provided to the fingerlings. From July 14th onwards, a marked reduction in feeding was observed, coinciding with an increase in temperature followed by increasing mortality rates (Figure 5). Subsequently, the feed intake diminished to minimal levels, likely reflecting a physiological response to temperature stress. The mortality peaked on July 21st following the high temperature of 38.0˚C recorded on 18th July. Pathological investigations revealed ocular and cranial hemorrhages, accompanied by scale and skin damage, presumably due to the stress caused by the unusually elevated temperatures. Following these events, the remaining 30,000 fish were harvested and relocated to the temperature controlled indoor nursery to conserve the remaining fish stock. Conclusions Although spawning was successful, the hatching rate was low, suggesting insufficient nutrition of broodfish, which in turn possibly affected embryonic development. Future trials should focus on the proper control of broodfish nutrition under captivity. In general, the survival rate achieved in the larval and nursery phases in this trial is encouraging and demonstrates the possibility of successful mass production of black spot snapper fingerlings in captivity, giving an impetus to the current restocking programs of the centre aimed at natural resource conservation (Table 2). However, in the cage farm, the fish were observed to be under great physiological stress due to the harsh environmental conditions (high temperature) of Abu Al Abyad Island waters. In this initial trial FIGURE 4. Fingerlings of Black Spot Snapper. FIGURE 5. Black spot snapper mortality in the cage in relation to temperature. TABLE 2. Larval rearing of Black Spot Snapper in 15 T tanks. Tank no Stocking Density Number stocked Age at harvest (days) Number harvested Survival (%) 1 10 150,000 37 28,000 18.70 2 9 140,000 34 19,700 14.10 3 8 120,000 33 8,700 7.30 Total 410,000 47,800 11.70 (CONTINUED ON PAGE 78)
RkJQdWJsaXNoZXIy MjExNDY=