By Mark Drawbridge *
The workshop was designed as an education, training and discussion platform focused on feeds and feeding strategies for larval marine fish with applicability to other marine and freshwater organisms that are fed. It was organized by experts from the National Oceanic and Atmospheric Administration (NOAA), United States Department of Agriculture (USDA), Oregon State University (OSU), University of California Davis (UCD), and Hubbs-SeaWorld Research Institute (HSWRI). The workshop represented an extension component of a recently-completed three year collaborative research project funded by the Western Regional Aquaculture Center (WRAC). The workshop incorporated lectures with hands-on learning activities with marine fish of different life stages from eggs to juveniles. Recognizing that nutritional approaches to larval rearing success must be coupled with other sound husbandry practices, the agenda covered a broad range of topics from broodstock husbandry to microbial management strategies.
A total of 27 people participated in the workshop, representing growers of cobia, Seriola, drum, flounder, sablefish, pompano, snapper, and marine ornamentals. Perhaps not surprisingly, the discussion periods revealed common challenges facing U.S. producers – either intermittantly or ongoing. As I reflected on these challenges and others that have been presented, I decided it might be appropriate to put together a wish list of needs that would make hatchery life “simple”, or at least more predictable.
The broodstock section of the workshop agenda covered systems design, basic husbandry, spawning methods, and egg quality components. Given the wide range of reproductive strategies in fish, including size at maturity, fecundity, courtship behavior, etc, much of this section is quite specialized for the particular species. Regardless, the end game is the same – producing adequate numbers of high quality eggs on a schedule that meets production planning needs. Broodstock nutrition is often questioned when egg or larval quality is less than what has been historically documented. For many large marine food fish species, the diet is comprised of fresh fish, squid, shrimp, etc, supplemented with vitamins. This is less than ideal given the potential for a breach in biosecurity, as well as the variability in quality, composition, and availability of some of these wild products. So, top on the wish list for this category would be customized (species-specific) dietary formulations for the broodstock species in question. This might include formulations that correspond to spawning and non-spawning periods, as appropriate. Recognizing the need for very large pellet sizes but modest volume (corresponding to a modest industry size), the formulation would most likely be mixed and manufactured into “sausages” on site. If polled, the group would also wish for easy, accurate, consistent measures of egg and larval quality.
At the workshop, approaches to larval nutrition were partitioned into the live and formulated feed stages, with a discussion of approaches to co-feeding. The live feeds section of the workshop included copepods, rotifers, Artemia, as well as associated enrichment strategies. Participants acknowledged challenges with systems and protocols that yield consistent mass production of each prey type, with the level of difficulty decreasing as the prey size increased. Challenges with commerically available enrichments and other additives included proprietary and non-customized formulations as well as availability in some cases. Initially, it would be greedy to wish for microdiets that could completely replace these live prey items, so a compromise would be custom live prey enrichments that are manufactured and supplied locally, as well as appropriate microbial control additives to support the live feeds production process.
The workshop section on microdiets included formulation and manufacturing processes that were shared with participants in a video format that greatly enhanced the learning experience. Research methods and results were also shared among the participants, including the use of novel feed markers to track ingestion; novel delivery methods for incorporating specific nutrients into live prey and formulated diets; development of open formula feeds; testing of different food particle types and associated manufacturing processes; and behavioral methods in larval nutrition research. Workshop participants acknowledged similar challenges with formulated feeds as those identified for live feeds. Specifically, lack of custom formulations coupled with proprietary commercial formulations, and unreliable availability of marine diets from overseas. So, custom formulated microdiets that are manufactured and supplied locally would be high on the wish list.
The microbial management component of the workshop focused on the importance of understanding and controlling bacterial communities within larval rearing tanks. Methods to do this were presented including bacterial quantification and identification, water filtration, biosecurity, passive larval transfers, self-cleaning larval tanks and other general hatchery methodologies for disinfection. The participants agreed that it would be beneficial to standardize the techniques for quantifying bacteria in an aquaculture setting in order to compare microbial monitoring results among producers.
Fortunately, there is research going on in all of these important culture areas, so progress is being made across the industry. The information gained from the demonstrations, presentations, and discussions during the workshop was invaluable. Being able to communicate findings on a regular basis was a desire expressed by participants during the workshop’s wrap-up session. So, the final item on the wish list would be the ability to hold similar marine larval workshops in the future – perhaps every 2-3 years. Workshops like these will allow for greater collaboration and potentially faster answers to the difficult questions that marine fish culture presents.
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.