By Mark Drawbridge
The associated article on yellowtail farming in Chile by Kolkovski and Lacamara covered the current production process at one advanced commercial operation in good detail and also described future R&D needs. Vargas provided a focused article on a seemingly simple decision of what tank color to use in larval rearing of a given species. Finally, Sims gave a status report on open ocean mariculture from a recent offshore aquaculture conference held in Turkey. Each of these articles was thought-provoking in its own way, and inspired me to use them as a springboard for further thoughts and discussion from our experiences at Hubbs-SeaWorld Research Institute (HSWRI) in California, U.S.A.
The title of this piece came to me as I thought more about what I had read in the above-mentioned articles and gave consideration to the state of the industry in general. All professions come with varying degrees of challenges and rewards (aka failures and successes), and marine fish farming is no different. The recipe for success is complicated depending on various economic, political/regulatory, and technical factors. Being such a relatively new industry, marine finfish farming is skewed toward the challenges, which is great for those with a pioneering spirit but not necessarily so for investors. As a research scientist I spend my days focused on the technical ingredients for success, which necessarily includes a strong awareness of the economic realities of production at various scales. As someone who oversees a commercial-scale research hatchery, I also have a keen awareness of political and regulatory considerations for egg-to-plate farming. In the U.S. this process has been paralyzed in the experimental phase along the continuum of experimental-pilot-commercial project scaling, at least when it comes to efforts to farm offshore. Applying a “never give up” spirit, we have sought to overcome this paralysis by testing various species of fish, diets and cage systems in the neighboring waters of Mexico. Other U.S. companies have done the same.
As indicated by Kolkovski and Lacamara, one of the challenges of breeding large pelagic fishes (i.e. 15-30kg each) is the large tank volume required for natural spawning. The large volume translates into greater space, maintenance, and operational requirements. We have good success breeding species like yellowtail, white seabass (Atractoscion nobilis) and California halibut (Paralichthys Californicus) in tanks of 40-140 m3. Working in southern California, we are invariably limited by space, so we often wonder how small of a breeding tank can successfully be used for a given species. The depth of water required for courtship and spawning is a related question of interest. Of course if it is critical to get lots of high quality eggs from a population, it is always best to err toward large, deep tanks! We recently went back and forth with a population of halibut that spawned well in a tank of 40 m3 but not well in a tank of 11.5 m3. They are now back in the 40 m3 tank and spawning productively once again. We have not been able to try 20 and 30 m3 tanks for this species but it would be interesting! One of the research projects we have just started will examine the effects of dietary manipulations of yellowtail broodstock on egg and larval quality. In order to compare treatment diets to controls with replication, we are planning to use 4 to 6 tanks. Our space limitations have us working with 10 m3 tanks once again (4m diameter X 1.1 m deep). The fish are mature but relatively small, averaging 10 kg; they are also currently spawning in 20 m3 tanks of the same depth. This experience, coupled with other anecdotal information from colleagues, leaves us optimistic for our study and its implications for future studies on reproduction in large pelagic fishes!
The article on selecting tank colors by Cecilia Vargas was excellent and leaves little to add. The visual environment perceived by the larvae is complex and should be optimized to maximize culture performance. The complexity includes the interplay among tank color, light intensity and wavelengths, and levels of turbidity. The effects of these factors on larval fish are also known to vary among and within species at different developmental stages, which further complicate the path to optimization. We have studied this extensively and still have much to learn and apply. One key performance measure in optimizing the visual environment of fish larvae is feeding efficiency (e.g. through improved prey contrast), which usually translates directly to larval growth and general health. Behavioral orientation by the larvae in the water column is also important to avoid contact with the tank bottom where bacterial contamination becomes a problem, as well as with the tank walls where the larvae can be physically damaged. In this regard, growth and survival are good metrics for experimental work but assessments of malformations should ideally be included as a quality metric.
As referenced by the previous authors, bacterial contamination can cause major problems in larval rearing. Obvious potential vectors are the eggs, water, live feeds and turbidity additives (e.g. algae). Common mitigation strategies are routine disinfection of eggs and the seawater supply, and periodic disinfection of all associated systems. Good hygiene in the production of live feeds is crucial to success. Using a turbidity agent like clay is becoming more common for some species because it has antibacterial properties, unlike algae that can often enhance bacterial growth. Another husbandry-related method of bacterial control is to gently transfer the eggs and larvae from their (colonized) culture tank to a sterilized tank one or more times during the culture process. As we have learned, new technologies like continuous, self-cleaning tanks are also being applied in places like Chile. Finally, following the lead of other aquaculture industries like shrimp, probiotics can be used to out-compete harmful bacteria when applied under appropriate conditions.
I will wrap this article up by saying that this discussion is the “tip of the iceberg” in the development of reliable culture methods for a given species leading to successful commercialization. The market value of the species will dictate how much leeway there is in the cost of production but competition among producers will always fuel the need for refinement toward optimization. Those involved in marine finish aquaculture are the “new kids on the block” from a historical aquaculture perspective, so the learning curve is still somewhat steep. I personally enjoy that aspect, although it does come with its share of frustrations. Then again, if it were easy, everyone would be doing it!
Mark Drawbridge has a B.S. degree in biology and a Master’s degree in Marine Ecology. He’s currently a Senior Research Scientist at Hubbs-SeaWorld Research Institute in San Diego, where he also serves as the Director of the aquaculture program.