As aquaculture production continues to produce more seafood than wild fisheries landings, diversification of finfish aquaculture is an important strategy to increase resiliency in food systems and provide farmed alternatives to some unsustainable fisheries. Unlike fisheries, finfish aquaculture is dominated by relatively few species with some being associated with environmentally unsustainable practices such as the use of wild fish derived feed ingredients and reliance on juvenile wild fish stocks to supply aquaculture grow out operations. Of interest to this study is the declining freshwater eels (unagi) fishery due to overfishing. While aquaculture practices may supplement the fishery, full life cycle sustainable unagi aquaculture has been difficult to achieve thus far due to their carnivorous diet and complex lifestyle.
Monkeyface pricklebacks (Cebidichthys violaceus) have potential as an alternative cultivated finfish, possessing a number of characteristics warranting an assessment of the species that includes herbivory, sedentary behavior, no fishery competition, and a possibility to be substituted for the declining fishery product-unagi. Though not technically an eel, C. violaceus is eel-like in appearance and is reported to taste like unagi. Their herbivorous ecology has the potential to facilitate the use of fish free feeds. However, it is unknown how efficiently C. violaceus will grow on a formulated feed, and if any diet ingredients cause adverse health effects. To test this, we conducted a controlled feed study by rearing juvenile pricklebacks on whole seaweed (control) and three different formulated pellet diets with varying amounts of seaweed and soy protein concentrate: algae pellet (3 types of seaweed), a mixed pellet (seaweed and soy protein concentrate), and a terrestrial plant pellet (soy protein concentrate and 10% Nori for palatability). Throughout the four-month study, we measured individual growth, the metabolic cost of digesting a pellet (specific dynamic action), and digestion efficiency.
Preliminary results indicate growth rates of monkeyface pricklebacks were statistically similar among the feed treatments, although growth tended to be highest on the mixed pellet feed. Additionally, the feed conversion ratios (FCR) between pellet treatments were lower on the soy-based pellets. In effect, monkeyface pricklebacks are capable of growing on a pelleted feed that is fish free.