Pumpkin seed cake as a fishmeal substitute in fish nutrition: effects on growth performance, morphological traits and fillet colour of two freshwater salmonids and two catfish species

ABSTRACT

The objectives of this study were to investigate the digestibility of pumpkin seed cake (PSC) for the rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), and effects on performance and product quality traits of four different fish species when PSC partially replaced fishmeal in extruded diets. A digestibility trial was carried out to determine apparent digestibility coefficients (ADC) for crude protein (CP), ether extract (EE) and gross energy (GE) of PSC fed to rainbow trout. In subsequent growth trials, effects on performance and morphological traits and fillet colour values of four different fish species [rainbow trout; brook trout, Salvelinus fontinalis (Mitchill, 1814); African sharptooth catfish, Clarias gariepinus (Burchell, 1822); and wels catfish, Silurus glanis (Linnaeus, 1758)] were evaluated when 60% of fishmeal protein of a reference diet was replaced by PSC protein (based on digestible CP). Nutrient ADC of PSC were high (CP: 89%, EE: 88% and GE: 84%). No significant effects on growth and only minor effects on fillet colour were detected in the trials. However, replacing fishmeal with PSC at the chosen level affected morphological traits and feed conversion in all four species to different extents. Replacement effects of PSC should be tested at lower levels of inclusion before conclusions are drawn on its suitability in fish diets.

KEYWORDS:

• African sharptooth catfish
• brook trout
• oilseed cakes
• performance
• pumpkinseed
• rainbow trout
• wels catfish

Acknowledgements

We are deeply grateful to Manuel Geiser, Adrian Feiler, Kristian Anicker, Jonas Kaufmann, Marcus Zielasko, Kay Lübke and Lars Müller from the Bavarian State Research Center for Agriculture – Institute for Fisheries (Starnberg, Germany), and Oxana Tyapkova from the Fraunhofer Institute for Process Engineering and Packaging IVV (Freising, Germany), without whose help the present study could not have been realised.

We would also like to thank the Technikum-team from Amandus Kahl GmbH & Co. KG (Reinbek, Germany) for preparation of diets for the growth trials.

Disclosure statement

No potential conflict of interest was reported by the authors.