Amending Reduced Fish Meal Feeds with ‘Conditionally Essential' Nutrients to Improve Performance of Hybrid Striped Bass

Replacement of fish meal (FM) with alternative proteins like soybean meal (SBM) can alter the physiological status of fish resulting in reduced production performance.  Alternative proteins may lack certain nutrients, e.g., phospholipid or tryptophan, which are associated with regulation of and recuperation from the generalized stress response.  Accordingly, we evaluated the growth performance and stress response of hybrid striped bass fed a 30% FM (30% SBM) control feed or a reduced FM feed (10% FM and 66% SBM, previously associated with eliciting heightened stress responses) as-is or supplemented with soy-derived phospholipid (Soy PL, 2% or 4%), marine-derived phospholipid (Marine PL, 2% or 4%), tryptophan (1% or 2%), or a tryptophan (1%) and soy PL (2%) blend.   Fish (33.3 ± 0.6 g, mean ± SEM) were stocked into a 36-tank recirculation system (8 fish/tank, 4 replicate tanks/treatment) and fed assigned diets once daily to apparent satiation for 9 weeks.  At the end of the feeding trial, fish were subjected to a low-water stressor challenge.  After 9 weeks of culture, survival (100%) and FCR (1.17 ± 0.02) were unaffected by dietary treatment, but weight gain, specific growth rate, and feed intake were affected by dietary composition.  Fish fed the 10% FM feed exhibited the lowest growth performance, whereas the 10% FM feeds supplemented with phospholipid and/or tryptophan exhibited improvement in growth performance depending on the specific nutrient and supplementation level.  Specifically, fish fed the 10% FM diet supplemented with 4% Marine PL demonstrated the highest weight gain (345 ± 8%), specific growth rate (2.40 ± 0.04 %BW/day), and intake (2.98 ± 0.08 %BW/day), marginally outperforming fish fed the 30% FM control feed.  The low-water challenge did elicit increases in circulating glucose levels (unstressed = 62 ± 5 mg/dL, stressed = 94 ± 5 mg/dL) following stressor exposure.   Although contrary to previous studies, dietary treatment had no significant effect on the following parameters:  glucose, hematocrit, or plasma lactate, osmolality, or ammonia, prior to or following stressor exposure.  Although dietary composition did not appear to influence stress tolerance in our study, supplementing reduced FM feeds with ‘conditionally essential’ nutrients, particularly marine-origin phospholipid, may yield greater growth performance in hybrid striped bass.