Hybrid Striped Bass Morone chrysops x M. saxatilis are popular sport- and food-fish commonly reared in the U.S., and have been exported for culture in the East (particularly Taiwan), Middleast, and Europe. Hybrid Striped Bass are typically reared on diets containing considerable amounts of both fish meal and fish oil. Fish meal sparing research has suggested that Hybrid Striped Bass accept a range of alternative, terrestrial-origin protein sources, including grain distillers dried yeast (Gause et al. 2011a, 2011b). However, in these cases, fish oil was commonly used as the primary dietary lipid source.
Like other carnivorous fishes, Hybrid Striped Bass reportedly require (n-3) long-chain polyunsaturated fatty acids (LC-PUFAs) in the diet, and expectedly exhibit reduced performance when LC-PUFA-rich fish oil is replaced with LC-PUFA-deficient alternative lipids (Lewis and Kohler 2008; Trushenski 2009), except in cases when the diet is particularly rich in fish meal (Wonnacott et al. 2004; Lane et al. 2006).
Limited previous research has demonstrated that fish meal and fish oil sparing influence Hybrid Striped Bass performance in a largely independent fashion (Trushenski and Kohler 2011), but there is still the need to comprehensively assess joint marine ingredient sparing in developing least-cost Hybrid Striped Bass feeds.
Accordingly, we evaluated the growth performance and fillet fatty acid composition of Hybrid Striped Bass fed diets containing principally marine-origin ingredients (fish meal, fish oil) vs. those containing principally terrestrial-origin ingredients using a factorial experimental design.
Twelve diets were formulated to test the effects of dietary protein and lipid source on Hybrid Striped Bass production performance and tissue composition following a 2 × 6 factorial design (Table 1).
Diets contained menhaden fish meal (FM) or grain distillers’ dried yeast (GDDY) as the principal protein source, and menhaden fish oil (100 FO) standard soybean oil (100 STD SO), fully hydrogenated soybean oil (100 HYD SO), vegetable oil refinery lipid (100 VO REF), or blends of the standard and hydrogenated soybean oils (67 STD SO/33 HYD SO, 33 STD SO/67 HYD SO) as the principal lipid source.
A recirculating aquaculture system was stocked with juvenile fish (~38 g) and each diet was fed to triplicate tanks of fish for 10 weeks.
Results and Discussion
Previous research has demonstrated that Hybrid Striped Bass perform well on reduced fish meal diets containing a variety of different alternative protein sources. In the present work, diets containing GDDY yielded greater feed intake and superior growth, regardless of lipid source (Table 3).
At higher inclusion rates (~36-50%), grain distillers dried yeast-based feeds yield reduced performance in Hybrid Striped Bass, but at more moderate inclusion levels (~13-27%) like that used in the present work (15%), grain distillers dried yeast appeared to enhance feed consumption and growth (Gause and Trushenski 2011a, 2011b; Trushenski and Gause 2013).
Grain distillers dried yeast has also proven similarly effective when incorporated at moderate rates in feeds for Rainbow Trout (Hauptman et al. 2014) and Pacific White Shrimp (Achupallas 2013). Thus, the improved performance we associated with partially sparing fish meal with grain distillers dried yeast in the present work is consistent with previous testing of this ingredient in aquafeeds.
Fillet fatty acid profiles were also significantly affected by protein source, lipid source, and interactions between the main effects. Higher levels of saturated fatty acids (SFAs), LC-PUFAs, and (n-3) fatty acids were associated with feeding marine-origin ingredients (FM > GDDY; 100 FO > all soy lipid sources), whereas higher levels of C18 PUFAs and (n-6) fatty acids were associated with terrestrial origin ingredients (GDDY > FM, all soy lipid sources > 100 FO).
Coefficient of Distance (Djh) values can be used to readily integrate differences in levels of numerous fatty acids to provide a simple description of how much one profile deviates from another.
According to this calculation, a Djh value of zero indicates perfect congruence between fatty acid profiles, whereas larger values indicate greater compositional differences between the tissues. Fillet Djh values ranged from 3.4?28.0, indicating varying degrees of fatty acid profile distortion among the experimental dietary treatment groups in comparison with the FM/100 FO group (Figure 1).
A larger range of Djh levels was observed in comparing corresponding diets in the FM versus GDDY series (e.g., FM/100 FO vs. GDDY/100 FO treatment, FM/100 STD SO vs. GDDY/100 STD SO) than in comparing the diets within these series (e.g., FM/100 FO vs. FM/100 STD SO vs. FM/100 HYD SO, etc.; or GDDY/100 FO vs. GDDY/100 STD SO vs. GDDY/100 HYD SO, etc.) suggesting that lipid source has a greater effect on profile distortion than protein source.
It is well-documented that the tissue fatty acid profiles of fish are affected by dietary fatty acid intake, and the influence of diet on tissue composition of Hybrid Striped Bass has been demonstrated many times using various dietary lipid sources. However, dietary fatty acid composition does not directly or proportionately influence tissue composition in all cases.
Menhaden fish oil contains relatively high levels of LC-PUFAs, especially 20:5(n-3) and 22:6(n-3), and Hybrid Striped Bass fed the fish oil-based feeds exhibited the highest levels of LC-PUFAs within their fillets.
Standard soybean oil contains no LC-PUFAs, but is rich in 18:2(n-6); and fillets of fish fed diets containing standard soybean oil became enriched with 18:2(n-6) at the expense of LC-PUFAs.
Vegetable oil refinery lipid, being primarily soy-based, yielded similar results. Hydrogenated soybean oil doesn’t contain LC-PUFAs either, but instead contains high levels of 18:0; however, 18:0 did not become significantly enriched in fillets of fish fed these diets and only a marginal reduction in fillet LC-PUFAs was observed.
Moreover, the degree of tissue profile distortion, as indicated by Djh values, was markedly lower among fish fed the hydrogenated soybean oil-based feeds. Similar results have been reported in previous investigations of hydrogenated soybean oil and other SFA-rich lipids in aquafeeds for Hybrid Striped Bass and other taxa (Trushenski et al. 2008; Trushenski and Kanczuzewski 2013; Kanczuzewski and Trushenski 2015; Trushenski et al. 2015). Given the apparent strategic advantage of hydrogenated soybean oil over other alternative lipids, there is growing interest in using this and similar feedstuffs in aquafeeds. We have advocated caution in incorporating these ingredients at high inclusion rates, given that digestibility may be a limiting factor for SFA-rich lipids (Kanczuzewski and Trushenski 2015). We believe some degree of caution is still warranted, however, the absence of negative, lipid-related effects on growth in the present case is encouraging.
We previously investigated sparing of marine feedstuffs with poultry byproduct meal and poultry fat in Hybrid Striped Bass (Trushenski and Kohler 2011) using a factorial approach similar to that used in the present work. We previously concluded that the effects of dietary lipid source and dietary protein source on fillet fatty acid composition were, in essence, the same: both were the result of shifts in dietary fatty acid composition. When fish oil is replaced with an alternative lipid source such as poultry fat, the fatty acid composition of the feed is altered. Although the effect is less overt, replacing fish meal with an alternative protein source such as poultry byproduct meal also affects the fatty acid composition of the feed via the small amounts of residual lipid that are present in both protein meals.
The present work illustrates the same principle: switching dietary lipid sources (i.e., fish oil and the soybean-derived lipids) substantially alters the fatty acid composition of the feed and, in turn, the fillets (with the exception of the hydrogenated soybean oil-based feeds noted above); switching other ingredients which contain some lipid (i.e., fish meal and grain distillers dried yeast) will have a similar, though less dramatic effect on dietary and tissue composition.
As noted by Trushenski and Kohler (2011), the effects of fish oil sparing and fish meal sparing on tissue composition in Hybrid Striped Bass are statistically independent, but also causally linked by the fatty acids contained within these ingredients and their alternatives.
In conclusion, our experiment provides further evidence in support of Hybrid Striped Bass’s acceptance of a range of dietary protein and lipid sources, the largely independent nature of fish meal and fish oil sparing on growth performance and tissue composition of fish, and the utility of alternative ingredients such as grain distillers dried yeast and various soy-based lipids in feeds for Hybrid Striped Bass.
This article was taken from the February 2016 Sustainable Aquaculture Digital.