Abstract
Using black soldier fly larvae meal (BSFM) in place of fishmeal is an ingenious strategy for sustainable fish aquaculture. However, BSFM has not been evaluated for dusky kob (Argyrosomus japonicus), an economically important fish in South Africa. Therefore, this five-week study investigated the effect of partially replacing fishmeal with BSFM on feed utilization, growth performance, and blood parameters of juvenile dusky kob in a recirculating aquaculture system. Four diets were formulated by replacing fishmeal in a commercial dusky kob diet with BSFM at the rate of 0 (BSFM0), 50 (BSFM50), 100 (BSFM100), and 200 g/kg (BSFM200). Fish length and weights were measured weekly, while blood analyses were performed at the end of Week 5. For fish length and weight gain, there were neither linear nor quadratic responses in Weeks 1–4, while quadratic trends (y = 14.77 (± 0.19)−0.11 (± 0.05)x + 0.01 (± 0.00) x2; R2 = 0.35 and y = 49.85 (± 1.53)−1.22 (± 0.39)x + 0.06 (± 0.02) x2; R2 = 0.47, respectively) were observed in Week 5 in response to BSFM levels. Quadratic effects (y = 1.75 (± 0.15) + 0.10 (± 0.04)x − 0.01 (± 0.00) x2; R2 = 0.39) were also observed for feed conversion ratio (FCR) in response to BSFM inclusion levels. Fish fed BSFM200 had a similar overall FCR and specific growth rate as those reared on BSFM0. All blood parameters fell within the normal range for the dusky kob. We concluded that 20% dietary replacement of fishmeal with BSFM does not compromise feed utilization and growth performance of juvenile dusky kob.
Highlights
Wild fish stocks are a major source of animal protein for humans, but they have largely remained static [1]
No previous studies have been carried out to evaluate the utility of insect meals in diets for dusky kob
The BSFM used in this feeding trial had higher protein content (550 g/kg DM) compared to BSFM previously used by Barroso et al [31] (362 g/kg DM) and Devic et al [32] (416.4 g/kg DM)
Summary
Wild fish stocks are a major source of animal protein for humans, but they have largely remained static [1]. Global fish consumption is increasing at a rate of 1.5% per year on a per capita basis, resulting in fish supply shortfalls [2] This can be addressed by expanding aquaculture. The growth of dusky kob aquaculture is mostly hampered by the high cost of fishmeal, a major dietary component [4], the supply of which is negatively affected by the static stocks of wild fisheries. The demand for fishmeal and fish oil on the South African market is high because it is used in diets of other farmed animals. This has driven the search for economically and environmentally sustainable alternatives such as black soldier fly (Hermetia illucens) meal (BSFM)
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