Effect of varied daily feeding intensities on growth performance and feed utilisation of South African dusky kob (Argyrosomus japonicus) juveniles reared in a recirculating aquaculture system

Several aquaculture studies have concluded that feed constitutes the heaviest cost in aquaculture enterprises. Consequently, researchers continue to investigate strategies that can lower feed costs such as the use of protein rich plant sources and insect meals to partially or completely substitute the expensive fishmeal in aquafeeds. However, this approach has often faced numerous challenges such as anti-nutrients in plant protein sources that limit their use and suboptimal polyunsaturated fatty acids profile in terrestrial protein sources such as insect meal. Precision feeding is a strategy that could also reduce aquafeed feed costs and enhance the economic sustainability of aquaculture. There is discordance regarding the feeding intensity that should be used for fish such as dusky kob. The current study was designed to compare the effect of three feeding intensities (2.8 %, 3.5 % and 4 % of body weight (BW)) on growth performance and feed utilisation of juvenile dusky kob (Argryrosomus japonicus). Dusky kob juveniles were randomly and evenly allocated to 18 tanks with a volume of 465 L. Each feeding intensity was randomly allocated to six tanks carrying 66 fish each. The average temperature and dissolved oxygen were 25°C and 5.5-6.0 mg/l, respectively. Commercial dusky kob diet was offered twice daily at the rate of 2.8%, 3.5% and 4% of body weight (BW). A feeding intensity × fish age (weeks) interaction effect was noted on fish feed intake (P<0.05) but not on weight gain, feed conversion ratio (FCR), and specific growth rate (SGR). The overall weight gain after six weeks of feeding was similar across the three feeding intensities (P>0.05). The 2.8% BW feeding rate promoted 1.06%/day SGR as compared to 1.21%/day and 1.48%/day for 3.5% and 4.0% BW feeding rates, respectively. Similar weight gains and FCR recorded across the three feeding intensities may suggest that the lowest feeding intensity (2.8% BW) should be used for dusky kob feeding to reduce feeding costs.