Apparent digestibility of raw materials by yellowtail kingfish (Seriola lalandi)

The apparent digestibility of 14 raw materials by yellowtail kingfish (Setiola Ialandi) was examined using the diet substitution method and yttrium oxide as the inert marker. Each raw material was examined in triplicate and faecal material was collected from fish using manual stripping techniques. All raw materials were tested at 30% inclusion, except for blood meal (BLM), which was tested at 15% inclusion. The reference diet was primarily composed of fishmeal (FM). The raw materials examined included: two sources of FM (FM-1; prime quality & FM-2; recycled tuna trimmings); poultry by-product meal (PBM-1 & PBM-2); lupin kernel meal (LKM-1 & LKM-2) and soy protein concentrate (SPC-1 & SPC-2) and a single source of krill meal (KRM), meat meal (MM), BLM, faba beans (FBM), corn gluten meal (CGM) and wheat flour (WH). With the exception of FM-2 and BLM, marine and land animal proteins were well digested, recording protein ADCs between 66.5 and 79.2%. The energy from marine and land animal proteins was also well digested, ranging from 67.0-83.5%, with the exception of BLM, which recorded a very low energy ADC of 43.0%. Digestibility of protein from plant sources was highest in WH (97.7%), LKM-2 (95.0%), FBM (94.7%) and LKM-1 (86.3%). The energy from LKM-1, LKM-2 and FBM was also well digested (67.4-76.9%); however, energy digestibility was poor in SPC-1 (35.5%), SPC-2 (31.7%), WH (34.0%) and CGM (19.4%). Generally, the ADCs recorded from plant proteins were greater variability than the ADCs recorded from marine and land animal proteins. Apparent digestibility of amino acids from marine and land animal proteins was fairly consistent and reflected the crude protein ADCs of these raw materials. The recorded ADCs of amino acids from plant proteins was more erratic and the error variance among replicates was higher than observed among replicated marine and land animal proteins. Mean ADCs of many amino acids were > 100% in FBM, LKM-2 and WH whereas the mean ADCs of amino acids recorded from YTK fed CGM were close to zero and in some cases negative. The results from this study indicate that yellowtail kingfish are generally efficient at digesting nutrients and energy from marine and land animal protein sources. Plant proteins such FBM, LKM-1 and LKM-2 appear to have relatively high protein and energy digestibility in yellowtail kingfish and may prove useful as alternative protein and energy sources in aquafeeds. The poor digestibility of the BLM and CGM used in this study suggests these products interfere with digestibility in yellowtail kingfish or there was some form of interaction between these raw materials and other raw materials in the reference diet. The ADCs derived for the raw materials examined in this study will assist in the formulation of research and commercial aquafeeds for this developing aquaculture species.