Performance of phytase-treated fishmeal-free and all-plant protein diets in pond production of market sized hybrid striped bass

Authors: Green, Bartholomew - Bart; Rawles, Steven - Steve; GAYLORD, T GIBSON - Us Fish And Wildlife Service; Schrader, Kevin; McEntire, Matthew - Matt; Webster, Carl

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2023
Publication Date: 9/18/2023
Citation: Green, B.W., Rawles, S.D., Gaylord, T., Schrader, K., McEntire, M.E., Webster, C.D. 2023. Performance of phytase-treated fishmeal-free and all-plant protein diets in pond production of market sized hybrid striped bass. Aquaculture. 577. Article 740006. https://doi.org/10.1016/j.aquaculture.2023.740006.
DOI: https://doi.org/10.1016/j.aquaculture.2023.740006

Interpretive Summary: Improved sustainability is a key goal for the aquaculture industry, especially with regards to reducing or eliminating fishmeal as an aquafeed ingredient. Temperate bass diets typically have included fishmeal. While hybrid striped bass have been reared on animal plus plant protein diets, they have not been reared on an all-plant protein diet. Formulated aquafeed also represents the largest phosphorus input to intensive aquaculture production systems and the volume and frequency of discharge from these systems is of concern globally given the role of phosphorus in eutrophication of receiving waters. In this study we demonstrated for the first time that hybrid striped bass can be grown market size in earthen ponds managed according to industry practices when fed a feed formulated with only plant proteins or with animal plus plant proteins. We also showed that dietary inorganic phosphorus can be replaced by diet phytase top-coating and judicious inclusion of plant proteins without negative impact on hybrid striped bass production. Dietary inclusion of phytase and elimination of inorganic phosphorus supplementation reduced phosphorus excretion to the pond environment by 40%.

Technical Abstract: We determined if ideal protein (IP) fishmeal-free (FMF) or all-plant protein (PP) diets of available ingredients could meet production needs of hybrid striped bass (HSB; Morone chrysops x M. saxatilis) grown to market size in ponds managed according to industry practices, and if phytase (Phy) superdosing (20,000 FTUs) could alleviate inorganic phosphorus supplementation. An off-the-shelf commercial feed (COM), an IP control diet containing 16% fishmeal (FM), and four IP test diets with or without phytase superdosing (FMF, FMF+Phy, PP, PP+Phy) were evaluated. Inorganic phosphorus was excluded from phytase treated diets. The IP diets were formulated at 37% digestible protein, 16% lipid, and supplemental Met, Lys, Thr. Hybrid striped bass (averaging 344 g/fish) were stocked (5,187 fish/ha) in 4 ponds/diet (0.1 ha) and grown for 5.5 months. Responses to FMF and PP (+/- Phy) diets were compared to the COM and FM control diets via Dunnett’s test, then as a 2x2 factorial. Most responses of the five ideal protein diets did not differ significantly (P > 0.1) from the COM. Only net fish yield, weight gain, and FCR of the PP diet were less than those of the COM diet. Fish fed FMF and FMF+Phy diets had higher fish yields, mean weights, and gains than PP and PP+Phy diets. FMF ponds had fewer than expected large (907-1,134 g) and more jumbo (>1,135g) fish and FMF+Phy ponds had fewer medium (680-906 g) and more large fish. PP ponds had fewer than expected jumbo fish. The COM diet resulted in larger livers (HSI), lower muscle ratio, but less feed phosphorus added to ponds compared to the FM diet. Absence of differences for other responses confirms the FM diet is a valid proxy for the COM diet. Phytase increased energy and protein retention of the PP diet but not the FMF diet. FM can be replaced with animal and/or plant proteins exclusively without major reductions in hybrid striped bass performance. The PP diet requires optimization of Met and branched chain amino acid levels to improve performance. Inorganic phosphorus can be replaced by diet phytase top-coating and judicious inclusion of phytate-phosphorus without negative impact on HSB production. Phytase superdosing of the FMF and PP diets did not improve production variables but did improve mineral retentions, more so for the PP diet. Phytase superdosing reduced feed phosphorus fed by 60% and pond phosphorus loading by 40% but requires optimization of inclusion levels and economic evaluation before recommendation.