Effects of commercial feeds and frozen trash fish on growth and hematological parameters of juvenile silver arowana Osteoglossum bicirrhosum

Silver arowana Osteoglossum bicirrhosum is a native species of the Amazon basin and presents opportunistic omnivorous habits with ichthyophagous preference. It is subjected to great fishing pressure for consumption and ornamental purposes. Fish farming for this fish is being developed, and one of the main difficulties is food availability for the different stages. This study assessed the effect of feeding with frozen trash fish and commercial feed on the growth and hematological parameters of juvenile silver arowana O. bicirrhosum. A total of 72 juveniles (74.2 ± 0.1 g) were randomly distributed into 12 net cages (6 fish per cage) and fed diets with different protein (P) and lipid (L) levels: frozen trash fish (52P:10L), and commercial tilapia (28P:4L), trout (40P:8L), and arapaima feed (50P:10L) with three replicates twice daily at a daily feeding rate of 6% of biomass for 90 days. At the end of the experiment, growth, hematological parameters, and cost per kilogram of weight gain were evaluated. The results revealed improved growth (P < 0.05) among fish fed with frozen trash fish (172.6 ± 26.9 g) and commercial arapaima feed (174.6 ± 48.8 g), in comparison with those fed commercial trout (120.5 ± 28.9 g) and tilapia feed (106.0 ± 37.1 g). Fish fed with frozen trash fish had lower daily feed intake (0.9 ± 0.1 g) and feed conversion ratio (0.8 ± 0.0), and greater hematocrit (36.2 ± 1.3%), erythrocyte sizes (348.7 ± 37.5 fL), total leukocyte (14.7 ± 0.3 × 10³ µL⁻¹), and lymphocyte levels (10.8 ± 1.1 × 10³ µL⁻¹) than juveniles that consumed the three commercial diets (P < 0.05). Feeding with frozen trash fish reduced (P < 0.05) the cost per kg of weight (USD 2.5) compared to feeding commercial diets for trout (USD 4.3) and tilapia (USD 4.8). The results show that feeding fresh frozen fish allows for healthy and less costly growth of juvenile silver arowana O. bicirrhosum.