WWW.WA S .ORG • WORLD AQUACULTURE • MARCH 2022 37 began exogenous feeding, it appears that the influence of broodstock diets was minimized based on growth performance (Table 3, Figs. 2 and 3). The initial differences in growth for fry from fish fed Diet 1, might have been due to bigger initial sizes due to lower stocking densities and thus competition for food, which allowed a higher individual weight (0.026 mg) compared to fry from fish fed Diets 2 and 3 (0.012 mg each). Even though survival rate in the nursery phase for fingerlings from fish fed Diets 2 and 3 were lower (63.0 and 65.4 percent, respectively) the total production of fingerlings was 175 percent and 156 percent higher than fingerlings produced from fish fed Diet 1. During the production cycle there were several instances of spinal deformities, including lordosis and swim bladder malformation, in fry (Figs. 4-9) and fingerlings (Figs. 10-11). This was likely a major contributor to mortality and included both lordosis (ventral curvature, V-shape) as well as kyphosis (dorsal curvature, V-shape). Broodstock condition/quality are factors that impact skeletal cells, cartilage and/or bone matrix development and bone mineralization in their progeny (Boglione et al. 2013a). Also, larval nutrition has been widely recognized as a key parameter that affects skeletogenesis during early fish development, particularly deficiencies/imbalances in some nutrients (lipids, amino acids, vitamins, and minerals) (Boglione et al. 2013b). The failure/ delay in swim bladder inflation can also cause deformities related to a hyperactivity of the larvae to maintain their position in the water column. In addition to nutrition and water current speed, factors affecting initial swim bladder inflation may also include gas saturation, photoperiod, light intensity, temperature and salinity. During this pilot study, two observations were clear: 1) malformed fry had inflated swim bladders (Fig. 12a-e, Fig. 13a-d), and 2) these pathologies tended to be less common in fry/juveniles that were spawned from fish fed Diet 2 and 3. These preliminary observations will require more thorough study with additional replicates. Nevertheless, it can be recommended that, in largemouth bass hatcheries, increasing the long-chain polyunsaturated fatty acid content, especially DHA, by top spraying with fish oil/microalgae oil onto a commercial diet (48 percent crude protein, 18 percent crude lipid) can be a simple approach to improve hatchery production and quality of largemouth bass fry and fingerlings. ( C O N T I N U E D O N P A G E 3 9 ) present, mats were removed and placed in hatching tanks (350 L), separated by dietary treatment. Samples (n =50) of eggs were collected frommats and measurements of egg diameter and the oil globule were made under a dissecting microscope. Fertilized eggs were incubated for five days before fry started hatching. After hatching, 50 fry were transferred into individual containers (0.5 L) in triplicate from each dietary treatment to assess survival over time when no food was provided. Daily observations of mortality were made. The remaining fry were held in hatching tanks for ten additional days before transferring to 1,000-L nursery tanks at 30 fry/L. Throughout this period, fry were fed rotifers Brachionus plicatilis and nauplii/ metanauplii of Artemia salina and gradually weaned onto artificial feed (Otohime B1 and Otohime B2), then only Otohime C1, before finally transitioning to pelleted feed. Pellet size was increased according to fingerling growth, from 0.8 mm to 1.2 mm, 1.8 mm, 2.5 mm, up to 3.5 mm. After eight weeks, fingerlings were harvested and growth production parameters were recorded. Results and Discussion Fecundity and hatching rates of largemouth bass were not quantified because we could not individually track the females. Nevertheless, the higher number of fry from broodstock fed Diet 2 or 3 suggests better fecundity and/or fry hatching rate. This observation could be linked to significantly larger eggs for fish fed Diet 3. Similarly, the oil globule diameter was significantly larger in eggs produced by fish fed Diets 2 or 3 (Table 2). To better evaluate fry quality, a starvation test was performed. In the control, 50 percent mortality occurred after 7 days and 100 percent mortality after 10 days. In contrast, more time was required for the fry to die in the experimental groups (Diets 2 and 3). A 50 percent mortality occurred after 9 days in the supplemented diet treatments while total mortality occurred after 11 and 15 days in the Diet 3 and 2, respectively (Fig. 1). Taken together, these results indicate that female broodstock fed Diets 2 or 3 deposited more nutrients in eggs. The greater deposition of nutrients could have been a decisive factor in the greater number of fry hatched from eggs produced by fish fed Diet 2 (150,324) and Diet 3 (129,422), compared to Diet 1 (57,129). However, once fry FIGURE 11. Largemouth bass from nursery (~4 g), V-shape. FIGURE 11. Largemouth bass from nursery (~4 g), V-shape.
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