Antagonists in plant-based feeds can have major impacts on the availability of many nutrients to aquatic animals, but particular attention has been paid to essential nutrients that are more prone to antagonistic interactions. Inorganic trace minerals (TM's) in the form of oxides and sulfates represent the bulk of TM supplemented to animal feeds, but their bioavailability can be diminished by antagonists such as phytic acid and other minerals. The objective of this 6-week study was to assess the responses of Pacific white shrimp (PWS) to fish meal (FM)- and soybean meal (SBM)-based diets containing different supplementation levels of manganese, iron, copper, zinc and selenium from inorganic or organic sources .
Eight experimental diets were formulated to contain 35% crude protein and 8 % lipid and different supplementation levels of the test TM's . Four diets (two FM- and two SBM-based) were supplemented with inorganic or organic TM's at 100% of typical commercial levels and two additional SBM-based diets were supplemented with the TM's at 50% of typical commercial levels. Two TM-unsupplemented diets and a commercial feed (CML) were used as controls for TM supplementation and diet performance , respectively. Each experimental diet and the CML were randomly assigned to four groups of 15 PWS juveniles ( individual mean weight = 3.3 ± 0.09 g) stocked in 110-L aquaria operating as a recirculating aquaculture system at a salinity of ~ 25 ppt. Shrimp in each aquarium were fed four times daily at a fixed rate of 0.59 g/shrimp/day and feed amounts to each group were adjusted weekly based on survival. Statistically significant differences between dietary treatments were considered at P < 0.05.
Shrimp grew at a rate of 1.22 to 1.74 g/week to a final mean weight ranging from 10.4 to 13.7 g and survival ranged from 78 to 95% . The overall ANOVA indicated no effects of SBM inclusion, TM source and supplementation level on shrimp production metrics, whereas CML- fed groups grew slower and displayed higher FCR compared to shrimp fed some of the experimental diets. Contrast analysis on speci fic treatments showed that: i) in TM supplemented groups, FM-based diets outperformed SBM-based diets in t erms of shrimp growth and FCR; ii) all TM supplemented groups performed similar to the respective TM unsupplemented control groups. Although these findings indicate that all experimental diets had adequate levels of TM's to support the production of PWS, overall FCR's were unexpectedly high ( from 2.2 to 3.1) and the study will be rerun.