Feed is an essential part of aquaculture. Firstly, as the nutritional benefits and the general health and robustness of fish depends mainly on the nutrients supplied through aqua feeds. Secondly, as feed is the most expensive part of fish aquaculture and availability of a cost-effective feed remains as one of the bottlenecks to achieve an adequate aquaculture sector development. The feed attributes to around 60-70% of the production cost . Due to fluctuations in supply and prices of traditionally used marine ingredients such as fish meal (FM) and fish oil (FO) , the aquaculture industry has inclined towards plant-based feeds. However, plant-based diets may result in deficient and imbalanced supply of essential nutrients, due to negative effects on palatability, and the presence of anti-nutritional factors on nutrient availability, which may also have other negative effects on fish health. Hence, to cover the nutritional requirements of fish, without compromising its health, and at the same time utilizing aquafeeds ingredients effectively, it is important to produce feeds with functional raw materials that could enhance the bioavailability and utilization of nutrients, which would lead to enhanced fish health and performance. In addition, it would enable the industry to save costs by improving feed efficiency. One such functional and sustainable marine ingredient is krill meal. The present trial was conducted to test the effect of krill meal inclusion towards enhancing the feed utilization and enhancing growth and nutritional in g ilthead seabream ( Sparus aurata ) juveniles.
Juvenile gilthead seabream (8.4± 0.04 g), were fed a practical diet with either a 15% FM/5.5%FO level of inclusion (KM0; control diet) or the same diet replacing FM by 20% (KM3; 30 g KM/kg diet), 33% (KM5; 50 g KM/kg diet) or 50% (KM7; 70 g KM/kg diet) Antarctic krill meal (KM) for 12 weeks in triplicates. At the end of the feeding trial, growth performance and feed efficiency were evaluated, and fish were subjected to a stress-challenge by confinement for 7 days. The omega-3 index (EPA+DHA% in RBC, which is used as an indicator of EPA+DHA% in the different tissues) was measured at day 0, 24 hours and after 7 days post stress.
F ish fed with KM5 and KM7 presented an improvement in FCR when compared to fish fed on conventional control diet with FM and FO (15% FM /5.5%FO). In particular fish fed KM7 and KM5 diets presented an improvement in FCR by a 6.5% and 4%, respectively when compared to control group. Besides, a relatively higher growth performance (3.5%) was observed in fish fed with KM7 diet in comparison to control group (Fig. 1). Further, the lipid efficiency ratio (LER) was significantly enhanced with all the 3 doses of krill meal (9% higher LER for KM3 and KM5 and 15% higher LER for KM7 , respectively, in comparison to control diet) and protein efficiency ratio (PER) was enhanced for KM5 and KM7 (3% and 7% higher PER for KM5 and KM7 diets, respectively) in comparison to control group. Omega-3 index was increased in all the three krill diets (4.3% increase in KM3, 4.7% increase in KM5 and 3.6% increase in KM7, respectively) in comparison to control group (1.2% increase) after 7 days post stress , indicating that nutrients in KM have the potential to possibly prevent the oxidation of vital polyunsaturated fatty acids, such as EPA and DHA and hence maintain the nutritional value of fish . These results demonstrate that krill meal inclusion leads to better utilization and retention of nutrients (fat and protein) in feed, and hence could significantly optimize feed efficiency , which provides economic benefits to farmers. Further, the inclusion or krill meal could enhance the nutritional value of fish as indicated through higher increase in EPA+DHA% (omega-3 index), and possible prevention of oxidation of EPA and DHA after oxidative stress, which would be beneficial for the consumers.