Lowered nutritional quality of prey decrease the growth and biomolecule content of rainbow trout fry.

Area of Science:

• Aquatic Ecology
• Fish Physiology
• Nutritional Science

Background:

• Dietary quality is vital for offspring development.
• Polyunsaturated fatty acids (PUFAs), including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are essential for fish fry.
• Freshwater ecosystems may experience shifts in zooplankton nutritional profiles.

Purpose of the Study:

• To investigate the impact of prey nutritional quality on rainbow trout fry growth and body composition.
• To determine how different diets, varying in PUFA content, affect trout fry.
• To assess the role of EPA and DHA in trout fry somatic growth and tissue composition.

Main Methods:

• A three-trophic-level experimental setup was used.
• Rainbow trout fry were fed artificial diets, marine zooplankton (DHA-rich), or freshwater zooplankton (Daphnia, DHA-deficient).
• Daphnia were cultured on diets of varying nutritional quality to manipulate EPA content.

Main Results:

• Trout fed fish feed or marine zooplankton showed complete muscle tissue replacement with dietary compounds.
• Fish fed any Daphnia diet exhibited only partial tissue renewal.
• Growth rates were five times higher in trout fed marine zooplankton compared to Daphnia diets, attributed to higher ARA, EPA, DHA, and amino acid content.
• Fatty acid isotope analysis indicated limited de novo synthesis of ARA, EPA, and DHA by trout fry.

Conclusions:

• Prey nutritional quality, especially DHA content, significantly influences rainbow trout fry somatic growth.
• Shifts in freshwater zooplankton communities towards DHA-poor species can negatively impact fish fry growth.
• Maintaining DHA-rich prey is crucial for supporting healthy fish populations in freshwater habitats.