Abstract
The main objective of this investigation was to test the effect of a standard commercial feed (Skretting Active ZA) on the growth performance of juvenile dusky kob (Argyrosomus japonicus), compared to the same feed when supplemented with six commercially available additives over a period of 10 weeks. A common additive in trial treatments contained two yeast strains (84% Candida utilis and 16% Saccharomyces cerevisiae) that were incorporated at 33% of the total feed mass. The yeast combined diet was also tested per se as a base experimental diet (BED). In the remaining five trials the BED was respectively mixed with selected herbal extracts or pharmaceutical probiotics to comparatively measure possible superimposed growth enhancement. Herbal extracts were Aquapro® (herbal powder), Liv-Up® (herbal granule), Liv-Up® (liquid) and UNBP-20® (liquid). The pharmaceutical 2-strain probiotic was Probiflora® (Lactobacillus acidophilus and Bifidobacterium bifidus). Experimental diets closely reflected comparative approximate nutrient values with respect to protein (46-48%), carbohydrate (17-18%), fat (14%) and fibre (11-12%) content. Juvenile dusky kob (n=50 per tank) of about 5.77±1.28 g were experimentally grown for 10 weeks in tanks (465 L) of a suitable recirculating aquaculture system (RAS) (24-25°C) with natural lighting. Supplement added diets induced a substantial average body growth of 43.3 g, except for slower (P<0.05) growth measured for the Live-Up®-liquid additive trial. The SGR was of the same magnitude between the BED and its complex with the mentioned additives. Also, the BED (46.5% protein) mediated a faster SGR (P<0.05) than the control diet without yeast (50% protein). The best FCR (0.95) was achieved with the BED added herbal product UN-BP20®. The dietary inclusion of the inactivated yeast types is recommended for dusky kob commercial diets since it showed enhanced growth performance and possible production viability.