Epsilon Archive for Student Projects

Abstract

Aquaculture is quickly expanding to meet global protein demand and has untapped potential to
provide food security for a growing human population. However, the most common protein sources
used to produce feed for farmed fish, fish meal and soybean concentrate, are associated with grave
environmental consequences. Thus, sustainable expansion of the fed aquaculture sector relies on
discovering novel protein sources. This study explores if white protein (WP) concentrate extracted
from alfalfa (Medicago sativa) through green biorefinery may be a promising alternative. A 47-day
feed trial was conducted on rainbow trout (Oncorhynchus mykiss) to assess the effect on physical
pellet quality, growth performance and fish health. Four experimental diets were produced: one fish
meal-based control diet (CTRL) and three diets replacing fishmeal with WP at 5%, 10% and 20%
of total feed composition content (WP5, WP10 and WP20). The WP20 diet was pre-extruded.
The physical pellet quality indicators tested were water stability, bulk density, expansion ratio and
pellet hardness. The WP20 diet had significantly higher water stability than all other diets in nearly
every period tested (30, 90 and 180 minutes), followed by CTRL, WP5 and WP10. As there is no
clear correlation between increased WP inclusion and increased water stability, the pre-extrusion of
the WP20 diet has likely improved its water stability properties. There were no significant
differences between diets in either bulk density or expansion ratios. However, the expansion ratios
gradually reduced with higher inclusion of WP, indicating pellets were more compact when
containing WP. Pellet hardness was also reduced as WP levels increased, meaning that pellets
containing WP were softer. The effect of pre-extrusion on physical pellet quality should be
investigated further.
No significant differences were identified between fish fed with the CTRL, WP5 and WP10 diets in
any of the fish growth performance indicators tested. However, gradual decreases in almost all
parameters tested were observed with increasing inclusion of WP. The WP20 diet had significantly
lower Fulton’s condition factor, weight gain, feed intake and SGR, and the highest FCR.
Furthermore, a gradual increase of WP in the feed formulations generated decreasing ADCs of dry
matter and crude protein. Future studies should further investigate the impact of WP on fish health
parameters. Yet, these results indicate that WP could be considered for inclusion in fish feed for
rainbow trout at 5% and 10%. Longer study durations with rainbow trout at varying life stages
should be performed to confirm these results.