Abstract
Farmed ballan wrasse (Labrus bergylta) is an efficient cleaner fish used for non-medicinal delicing of Atlantic salmon in sea cages replacing to an increasing degree wild wrasse due to considerations for biodiversity and risk of overfishing local wrasse populations. Farming of ballan wrasse has been hampered by low growth rates, high prevalence of skeletal deformities and other welfare related pathologies. In this study we investigated how diets identical in composition but differing in their technical characteristics, by being prepared using different feed production technologies, affect fish performance, mineralization, bone development and gut health of the ballan wrasse larvae and juveniles. The different production technologies include the commonly used ‘high temperature’ extrusion, cold extrusion, and agglomeration, resulting in feed pellets with distinctive physicochemical properties. The results revealed that prolonged feeding periods with extruded pellets during ballan wrasse larvae weaning result in low body mineralization and the development of severe skeletal deformities. In juvenile ballan wrasse, the extruded pellet treatment resulted in higher mortality rates, fish with larger livers, indication for increased serum TAG and cholesterol in a similar manner, and increased activity of the digestive enzymes LAP and maltase, most probably as a compensatory mechanism to the assumed reduced availability of protein and carbohydrates of extruded pellets for this fish species. Smaller dietary effects were identified in terms of intestinal morphology and gene transcription rates.
Highlights
Over the last decade, both wild and farmed cleaner fish, including ballan wrasse (Labrus bergylta), have been used as a tool in combating infestations of farmed salmon with sea lice, a parasitic copepod (Lepeophtheirus salmonis)
Bogevik et al (2016) suggested that ethoxyquin present in fishmeal and/or the secondary metabolites of fish oil oxidation may act as feeding repellents for the fussy ballan wrasse larvae, or mask the attractants deriving from the crustacean feed components
Ballan wrasse larvae are very sensitive to small dietary freshness differences which may result from processing on otherwise high quality marine raw materials (Kousoulaki and Opstad, 2012)
Summary
Both wild and farmed cleaner fish, including ballan wrasse (Labrus bergylta), have been used as a tool in combating infestations of farmed salmon with sea lice, a parasitic copepod (Lepeophtheirus salmonis). Though reaching up to 95 % weaning survival, feeding ballan wrasse larvae a fishmeal-free common ‘high temperature’ extruded weaning diet crumbles over a longer period resulted in almost 100 % head/jaw deformities (Kousoulaki et al, 2014b). This deformity may further hinder the ability of the fish to grow and become capable of removing salmon lice effectively. Additional sporadic observations have revealed that ballan wrasse larvae jaw-cranial deformities may not occur, or be less prominent, when agglomerated pellets are used instead of extruded crumbled pellets, or when fishmeal or the water soluble part of fish meal (stickwater) is included in the diet (Kousoulaki et al, 2014a;b). Ballan wrasse larvae are very sensitive to small dietary freshness differences which may result from processing (drying, pelleting) on otherwise high quality marine raw materials (Kousoulaki and Opstad, 2012)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
