Abstract
Five experimental diets were formulated to evaluate the effects of dietary enzymatically hydrolyzed tuna by-product on growth, non-specific immune responses, and hematology of juvenile rainbow trout (Oncorhynchus mykiss). A basal diet with 50% of fishmeal was used as control (CON) and four other diets replaced 12.5% (TBB12.5), 25% (TBB25), 37.5% (TBB37.5), and 50% (TBB50) of fish meal in the CON diet. Juvenile rainbow trout (4.87 ± 0.05 g) were randomly distributed into 15 tanks (50 L) and fed 3–4% of wet body weight two times a day. At the end of 7 weeks of feeding trial, weight gain, specific growth rate, feed efficiency, and protein efficiency ratio of fish fed CON diet were significantly higher than those of fish fed TB50 diet (P < 0.05). But there were no significant differences among fish fed CON, TBB12.5, TBB25, and TBB37.5 diets (P > 0.05). There were no significant differences in GPT levels among fish fed CON, TBB12.5, TBB25, and TBB37.5 diets. Also, there were no significant differences in lysozyme, superoxide dismutase, glucose, and total protein levels in all experimental diet (P > 0.05). The broken-line analysis indicated that the minimum dietary level of enzymatically hydrolyzed tuna by-product to replace fishmeal could be 29.7% in rainbow trout. These results indicated that the optimum level of dietary enzymatically hydrolyzed tuna by-product could replace greater than 29.7% but less than 37.5% of fishmeal in juvenile rainbow trout diet.
Highlights
Fish meal (FM) is the one of the most important ingredients used in aquafeed
Based on the results obtained in previous studies, the aim of this study is to partially replace FM with enzymatically hydrolyzed tuna by-products in order to examine the effects on growth and non-specific immune responses in juvenile rainbow trout
After completion of feeding trial, weight gain (WG), specific growth rate (SGR), feed efficiency (FE), and protein efficiency ratio (PER) of fish fed CON was significantly higher than fish fed TBB50 diet (P < 0.05)
Summary
Fish meal (FM) is the one of the most important ingredients used in aquafeed. FM is a high-quality source of protein and is desirable for its rich essential amino acids profile (Cho and Kim 2011; Anderson et al 2016) as well as for its vitamin and mineral content (IFOMA 2000). Because of the limited supply of FM coupled with its increasing demand, the cost of producing fish is likely to (2019) 22:1 tuna muscle by-product powder is a promising feed ingredient to replace 50% FM protein without reduction in the growth performance of olive flounder. Enzymatic hydrolysis is a process by which enzymes facilitate the cleavage of chemical bonds by water, playing a pivotal role in the digestion of food (Nielsang et al 2005). This process makes it possible to improve the nutritive value of individual feed ingredients (PER, digestibility and FCR). Replacement of FM in aqua feeds with inexpensive protein sources, such as unexploited by-products which are regionally or locally available, may be a great opportunity for sustainable resource utilization
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