The d emand for fishmeal and fish oil in aquaculture feeds, has increased dramatically in recent years . Alternative protein and oil sources are needed if further development of the aquaculture industry is to be sustained. Terrestrial plant ingredients can replace a portion of the fishmeal used in feeds for a number of species. Complete replacement, however, is seldom achieved . Macroalgae may prove a more appropriate feed ingredient than terrestrial plants products for marine fish feeds as macroalgae contains many essential nutrients from the marine environment that are limiting in terrestrial plants. Additionally, there appears to be health benefits associated with the use of some macroalgae species for some marine fish species. In previous studies at our laboratory , the addition of the red macroalgae Turkish Towel to sablef ish feeds improved liver health and increased fish survival when exposed to the pathogen Aeromonas salmonicida.
In this study, we incrementally added the red macroalgae Pacific Dulse to alternate plant based feeds for juvenile sablefish to evaluate the effect of this ingredient on fish growth, feed intake , feed efficiency, whole body nutrient composi tion, and liver condition . Five isonitrogenous feeds we re prepared with 0, 2.5, 5, 7.5, and 10 % dulse . As dulse was added , soy, corn, and wheat ingredients were proportionately removed from the diets. Dulse was sourced from Sol-Sea LTD , Seattle, WA, USA and was produced intensively in land based tanks in 2020.
Fish grew well during the 8 week the study with 100% survival. Feed intake increased non-linearly with the addition of dulse to the feeds and peaked at 5% inclusion (P =0.045 , Figure) . There was no effect of dulse addition on feed efficiency (P = 0.225 ). While not significant, fish weight gain mirrored feed intake and was numerically highest among 5% dulse fish (P =0.234) . There was no effect of dulse addition on fish length, condition factor, or hepatosomatic index. Effects on whole body nutrient retention and liver histology will be presented. Results from this research indicate Pacific Dulse may be a promising alternative feed ingredient for cold water marine fish . Further research is needed to explore reasons behind the observed decrease in feed intake with feeds containing over 5% dulse and to fully evaluate potential fish health benefits associated with this ingredient.