Rainbow trout can discriminate between feeds with different oil sources

Area of Science:

• Aquatic Nutrition
• Fish Physiology
• Animal Feed Science

Background:

• Dietary oil composition significantly impacts fish feed acceptance and nutritional value.
• Rainbow trout (Oncorhynchus mykiss) are a key aquaculture species with specific nutritional requirements.
• Understanding fish oil (FO) versus vegetable oil (VO) preferences is crucial for sustainable aquaculture feed development.

Purpose of the Study:

• To assess juvenile rainbow trout's ability to differentiate between isolipidic diets containing different oils.
• To determine rainbow trout's preference between fish oil and vegetable oil-based diets.
• To evaluate the impact of specific fatty acids (linolenic, linoleic, oleic) in vegetable oils on diet selection.

Main Methods:

• Two-choice feeding trials using self-feeders to present distinct diets.
• Diets included fish oil (FO) and vegetable oils: linseed oil (LO), sunflower oil (SO), or rapeseed oil (RO).
• Preference was measured by changes in feed demand, preceded by adaptation and followed by validation periods.

Main Results:

• Rainbow trout demonstrated a clear capacity to discriminate between FO and VO diets.
• A significant preference for the FO diet over all tested VO diets was observed.
• Dietary linolenic acid (LO) showed the highest avoidance (37-39%), followed by linoleic acid (SO, 30%), while oleic acid (RO) was best accepted (15-17% avoidance).

Conclusions:

• Juvenile rainbow trout prefer fish oil-based diets over vegetable oil-based diets.
• Excess linolenic and linoleic acids in vegetable oils may negatively impact feed acceptance in trout.
• Diet selection did not alter overall feed or energy intake, as avoidance of VO was compensated by increased FO consumption.