WWW.WA S .ORG • WORLD AQUACULTURE • MARCH 2022 35 ( C O N T I N U E D O N P A G E 3 7 ) Source of Broodstock In early April 2020, 180 pairs of largemouth bass were transferred from earthen ponds to a recirculating aquaculture system (RAS) in a commercial hatchery. The RAS consisted of three tanks (3,000 gal each), biofilter unit, mechanical filter, pumps, aeration and pure oxygen that was injected to ensure adequate dissolved oxygen levels were maintained. Sixty pairs of broodfish were placed in each tank at controlled water quality conditions (temperature 17.9 ± 0.7 C, dissolved oxygen 8.0 ± 0.5 mg/L, dissolved oxygen saturation 83.1 ± 4.5 percent) and photoperiod (10 h light:14 h dark). After acclimating broodstock, tanks were randomly assigned one of three dietary treatments. One group received a commercial diet (48 percent crude protein, 18 percent crude lipid) as control (Diet 1); the other two diets were top sprayed with fish oil (at 0.5 percent) and microalgae oil (at 0.5 percent) (Diet 2), and the other diet was also top sprayed like Diet 2, but also included a commercial nucleotide (400 mg/kg). The proximate and fatty acid composition of the diets were measured according to AOAC (2006) methods 996.06 (Table 1). At the end of the 92-d study, broodstock consumed similar quantities of diets: Diet 1 – 105.3 kg, Diet 2 – 102.5 kg, Diet 3 – 104.1 kg. Broodstock were then transferred to spawning tanks where the temperature was increased from 17.8 C to 20.3 C and photoperiod was increased to 12 h light: 12 h dark. Spawning tanks were supplied with mats (45.7 cm × 45.7 cm each). When eggs were FIGURE 5. 6 DAH larvae, normal first inflation. FIGURE 4. 3 DAH larvae, normal first inflation. FIGURE 7. 6 DAH larvae, V-shape and abnormal inflation SB. FIGURE 6. 5 DAH larvae, V-shape and abnormal inflation SB. FIGURE 8. 6 DAH larvae, V-shape and normal inflation SB. FIGURE 10. Laregemouth bass from nursery (~4 g). FIGURE 10. Laregemouth bass from nursery (~4 g). FIGURE 9. 12 DAH larvae, V-shape.
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