Feeding a hungry world; restoring depleted fish populations

The world’s population is slated to grow by 2.4 billion people by 2050.* According to the Food and Agriculture Organization of the United Nations, we must produce 70 percent more food to meet impending world hunger needs. As some wild fish stocks are decreasing, aquaculture is the practical solution to produce food sustainably, as well as to help replenish depleted fisheries. Aquaculture also can provide significant value to local economies. Reducing our country’s reliance on imported seafood would reduce the U.S. trade deficit and provide “blue tech” jobs to revitalize our working waterfronts.

Our research team and its collaborators have played a leadership role for over 35 years in developing innovative replenishment solutions with no negative biological impacts. Breeding and raising fish from minuscule eggs to a market-ready size is a complicated process. It requires invention and significant knowledge from many fields of science, including the understanding of sophisticated hatchery infrastructure to ensure an optimal environment for fish to flourish.

Whether we’re producing white seabass and halibut for release into the wild, or yellowtail, mussels or seaweed for the seafood market we are preserving and renewing wild stocks by providing supplemental sources of plants and animals that are produced sustainably.

Help us feed the world, replenish fish populations and provide economic value to American coastal communities.

Primary Research Areas

Long Term Eco-System Research


Marine Vertebrate Ecology

  • Whale Sharks
  • Cook Inlet Beluga Whales
  • Cannel Islands Seals & SeaLions
  • Green Sea Turtles
  • North American River Otter
  • Dolphins (Indian River Lagoon)
  • Fish Tracking

Research Diciplines 

  • Fish Nutrition and Health
  • Fish Physiology
  • Genetics
  • Advanced technologies and engineering
  • spawning and larval culture techniques
  • Environmental monitoring
  • Fish tagging and tracking
  • Population biology and modeling
  • Biological and ecological applications using cultured fish
  • Fish Behavior


Seabass in the Classroom


Mark A. Drawbridge, M.S.

Program Director, Senior Research Scientist

Mike Shane

Director of Fisheries Enhancement

Kevin Stuart, M.S.

Research Scientist

Connie Silbernagel, D.V.M., M.P.V.M.

Research Scientist II

Research Diciplines – In Depth 


Understanding the role of nutrition for each life stage of an organism under culture is an important factor for producing high quality fish for either replenishment or seafood production.  We have conducted extensive nutrition research on adults, larvae, and juveniles to be able to influence not only survival but to improve larval and juvenile quality.  At HSWRI we have begun studying broodstock nutrition and have the capabilities to run replicated trials on large pelagic species such as California yellowtail (Seriola dorsalis).  Larval nutrition is perhaps the most challenging because this life stage is so small and fragile, and organ systems are still developing.  Marine fish larvae are fed one or more live prey that are enriched to enhance their nutritional value before the larvae are weaned onto formulated diets.  This dietary regime and transition of food types adds to the complexity.  From a sustainability standpoint, the juvenile (growout) stage is very important because of the large biomass involved that requires substantial amounts of food.  Historically, diets for carnivorous species consisted of large proportions of fish meal and oil to meet the dietary protein and lipid requirements of the species.  With aquaculture growing so rapidly, those natural resources will become scarcer and more expensive.  Thus, the quest for alternative sources of oil and protein is an area we have studied extensively.


A comprehensive and viable fish health program is key to the success of any aquaculture enterprise because it extends into all aspects of hatchery operations at some level.  HSWRI maintains a Fish Health Management Team that meets routinely to discuss and evaluate issues related to fish health.  HSWRI’s approach to aquaculture begins with disease prevention, which is only possible when the culture requirements of the animal are well understood and accommodated to every extent possible, or when best management practices are employed for new species.

Research in the area of fish health at HSWRI has been varied over the years but can generally be categorized into 1) improving fish survival and quality, 2) identifying pathogens in cultured animals and determining appropriate treatment options, and 3) surveying wild fish populations to be able to understand their health status and relate it to the species in culture.  The importance of this work cannot be overstated relative to fisheries replenishment programs where cultured fish are intentionally released into the wild, and the corollary concerns surrounding accidental escapement of farmed fish from ocean net pens. 

Recently, we have instituted a semi-quantitative surveillance program of documenting skeletal malformations in larval and juvenile finfish at our marine hatchery as part of our fisheries replenishment program.  Goals of this surveillance program are to document cultured fish malformation incidence, assess morphologic variation between wild and cultured finfish species, and prevent the release of a hatchery fish phenotype.  Disease prevention and diagnosis is an important component for all finfish life stages, ranging from larvae to broodstock.  We consider all aspects of species history, environment, water quality, nutrition, husbandry, or stress as they may interact with potential pathogens that can result in finfish disease. We institute surveillance programs to track early indicators of non-infectious disease agents such as gas bubble disease, which are difficult to treat and can result in long-term vision impairment. We focus on strong biosecurity to prevent pathogen introduction and seek to improve animal welfare using new anesthetics with minimal withdrawal times, and to address the public health and safety of seafood consumers.


Research on fish physiology at HSWRI has ranged widely and often involved outside collaborators.  Understanding of physiological processes in cultured organisms is a component of fish health that is critical to optimizing husbandry conditions.  Until various physiological processes can be studied in detail, culturists often rely on trying to replicate the natural conditions those life stages are found to the extent that they are known and can be simulated.  Examples of physiological research we have been involved in can be gleaned from the reference list below.  This includes studies of the effects of gas supersaturation in juvenile white seabass, which are particularly susceptible.  Concurrent collaborative studies on the effects of exercise conditioning on growth, muscle development and stress tolerance also fall within this discipline.  Not well represented by our publication list are a series of studies designed to define the thermal preferences and tolerance limits of various species and life stages under culture.  This information is needed to optimize thermal regimes in recirculating systems where temperature is controlled and to avoid exposing species and life stages to temperature extremes in systems that cannot be controlled such as flow-through tanks or ocean cages. 


Genetic tools are applied throughout the Sustainable Seafood Program to improve the culture of organism for fisheries replenishment and seafood production.  First, genetic parentage analysis plays an important role in understanding the population dynamics of captive breeders (broodstock) and has been applied extensively by HSWRI with California yellowtail and white seabass.  This technique allows cultured offspring to be linked to the parental broodstock, thereby informing decisions that maximize reproductive output and performance (e.g. removing a breeding individual that is producing low quality eggs or larvae).  In a fisheries replenishment context, the known genetic makeup of the broodstock has the potential to be used as an identifier of offspring that have been released into the wild.  A genetic mark for cultured white seabass is currently being developed that would complement the existing marking approach using coded wire tags.  Genetic marking provides a lifetime mark (no tag loss), with no adverse handling or tagging effects, and can be detected non-invasively from a small fin clip.  As part of this project, archived biological samples (fin clips and otoliths) will also be used to retrospectively estimate the contribution rate of cultured white seabass to total catch and determine if coded wire tag loss has led to under-detection in the catch.

Fisheries replenishment requires rigorous broodstock management to maintain sufficient levels of genetic variability in cultured offspring intended for release into the wild.  For this reason, broodstock of both white seabass and California halibut maintained by HSWRI are composed exclusively of wild-origin individuals and are selected according to best available scientific information on the wild population structure (hatchery breeding groups reflect local sub-populations, where applicable).  Protocols have also been developed, using the parentage approach described above, for appropriate broodstock rotation and replacement schedules to meet this objective.  For seafood production, broodstock management to maintain genetic diversity is less critical as these offspring will not be released into the wild.  Instead, the focus is on selecting for traits of interest (e.g. fast growth, tolerance to specific environmental conditions).  Depending on the research application, California yellowtail broodstock held at HSWRI consist of mixed individuals (wild- and cultured-origin) or entirely culture-origin individuals (first and second generation).  Currently, a research area of interest is developing cold tolerant strains of California yellowtail that would perform well in cage culture off the coast of southern California.

Advanced technologies and engineering

As our production systems have moved from flow-through to recirculated, and scales of production have increased from experimental to commercial levels, the need to increase the efficiency and sophistication of systems has also increased.  As with many facets of aquaculture, life support systems technologies are continuously evolving.  Both HSWRI aquaculture facilities serve as testing grounds for new technologies and combinations of system components.  Gradually, component preferences are evolving for particular species and life stages.  Among the desired, if not required, attributes of these components are simplicity, durability (in seawater), reliability, effectiveness and efficiency.  In addition to “standard” recirculation system components, creative design approaches are being applied to develop species-specific systems for collecting brood fish, integrated fish grading and transfer, tagging, live feed production and delivery, monitoring and control, and integrated species systems.  We have also tested various cage designs in the offshore environment, including a submersible cage system.

One area of innovative research for us has centered on finding ways to mitigate gas imbalances in the environment and its effects on fish.  This has included developing portable hyperbaric chambers to offset barotrauma in brood fish collected from deep water, as well as customizing efficient but relatively inexpensive vacuum degassing systems to offset supersaturated seawater conditions that result in gas bubble disease.  Our hyperbaric chambers are now being used and replicated by other researchers and public aquariums to study and collect fish successfully from deep water.  Our research on chronic effects of supersaturation in white seabass continues and effective vacuum degassers are in the final stages of development and implementation.

Another recent example of our design and testing capacity is a larval tank project that we conducted in collaboration with Oceans Design, Inc.  In this project we developed a state-of-the-art, commercial-scale, self-cleaning larval tank that is now in commercial production.  The basic premise of this tank design was to include a motor-driven cleaning arm that continuously “sweeps” debris off the bottom and walls of the tank and into a trench that spans the radius of the tank.  This project was very successful and has led to an ability for owners to grow more fish per unit area with less labor. 

We are also currently expanding our fish culture to include marine algae and invertebrates in both flow through and seawater reuse configurations.  These different organisms are being combined in a rearing system in what is referred to as integrated multi-trophic aquaculture or simply IMTA.  In these systems, resource inputs are maximized as downstream trophic levels utilize solid and dissolved nutrients from the upstream organisms.  Waste solids can be 35% of the feed given to the fish, so recapturing this in the form of edible invertebrates represents a significant gain. Furthermore, by removing dissolved nitrogen and phosphorus from the system, macroalgae reduce the requirements for whole-system water exchange and thereby reduce effluent volume. This opens up possibilities for siting new farms and the information gained will be useful to growers who may be interested in diversifying their product line of seafood in an efficient manner that maximizes resource inputs.

Development of spawning and larval culture techniques

While this is not an obvious or traditional discipline of biology, within an aquaculture setting it is the basis for success or failure for any given species.  Someone in the supply chain needs to be able to reliably produce mass quantities of high quality fingerlings for growout.  Achieving this requires successfully spawning adults and rearing the larvae – two components of the culture process that often represent the greatest bottlenecks.  The importance of quality cannot be overstated when producing any life stage from egg to fingerling.  We have successfully spawned and reared a range of species, including being the first, and in cases the only, to successfully rear fingerlings of some species.  We have developed mass production techniques for California yellowtail, California halibut, and white seabass to the extent that these species could be commercialized today.  We have also successfully bred and cultured other species like California sheephead, starry rockfish, cabezon, kelp bass, and giant sea bass on an experimental basis.  While each species has their nuances when it comes to culture, many techniques that we have developed can be applied to other species to greatly reduce the learning and start-up curve.

Environmental monitoring

The environmental monitoring program at HSWRI has evolved from dual needs.  First, in initiating scientific studies of recirculation systems and associated components, it became clear that more sophisticated testing methods, yielding greater resolution and precision than typical colorimetric and photometric methods, would be desired.  Additionally, it was desirable to develop methodologies for accurately measuring less common or more technically challenging parameters in seawater (e.g. Total Volatile Solids, silicates, phosphates).  Even if samples are not tested in-house, coordination of sample collection and testing by outside laboratories is often required.

The second area of need has been for environmental monitoring of seawater and sediment quality associated with net pens.  Toward this end, well established monitoring protocols for salmon farms in the northwest were adapted to Southern California through training and mentoring of HSWRI staff by experts from that area.  Although not mandated by any regulations due to the small scale of HSWRI operations, having the techniques well established and having obtained baseline data from the net pens is proving to be extremely valuable.  Coupled with this capability to monitor existing farm sites is research directed toward selecting appropriate new sites, which involves working collaboratively with modelers and collecting pertinent data such as sediment characteristics and seasonal current information using acoustic Doppler current meters.

Fish tagging and tracking

The marking or tagging of fish is a fundamental fishery tool that our scientists employ to identify or differentiate our cultured fish from other individuals or groups of fish.  Since the late 1980’s the research we have conducted under our fisheries replenishment program has utilized various marking methods (e.g. streamer or spaghetti tags, chemical dyes, elastomer compounds) for our cultured fish that are released into the wild.  Additionally, these tagging methods are also used in tank studies to identify individuals as well as understand tag retention.  The most common tagging method that we employ in our replenishment program for white seabass, is the insertion of a tiny coded wire tag into the cheek musculature of each fish.  Each 1.1 mm length tag has a unique code etched on it that helps our scientists identify the hatchery-reared fish upon its recapture.  This tagging technology has helped the program to identify patterns of movement, dispersal, survival as well as wild prey items of released cultured white seabass through our fisheries independent and dependent sampling efforts.  We have recaptured white seabass that have been at liberty, in the Pacific Ocean, from just several days up to 20 years.  We have also recaptured them 160 km (100 miles) off the coast of San Diego and more than 550 km (340 miles) near the coast from their release location. 

Acoustic telemetry is another method that HSWRI researchers employ to understand the fine scale movements and dispersal of fish.  We implement this technology by surgically implanting a small acoustic transmitter (sound producing device) into the abdomen of fish.  Each transmitter generates a slightly different sound pattern that permits investigators to identify individual fish.  When fish are released into the wild their movements can be tracked either actively or passively.  When actively tracking, an underwater hydrophone (listening device) is deployed from a small vessel so that investigators can hear and follow the fish.  Passive monitoring utilizes moored underwater receivers that can detect, identify and store data on the receiver when a fish with a transmitter swims near them.  These receivers are deployed in various arrays in embayments and along the coastline.  Periodically HSWRI scientists retrieve and redeploy the receivers to download the data.  Some of the interesting science we have learned from using this technology includes identifying predators and patterns of emigration from embayments for the cultured white seabass we are releasing into the ocean. 

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