fish report header

The art (and policy) of sedation

February 17, 2014


Handling fish is an integral activity when it comes to conducting fisheries studies, and is therefore a daily part of our work. Studying fish entails measuring and weighing them, collecting scales from some, performing gastric lavage on others, and attaching or surgically implanting tags in a few. For most of these procedures, the use of sedatives is essential to minimize stress, facilitate handling, and reduce the risk of injury to the fish. The Federal Food and Drug Administration (FDA) strictly regulates the use of chemical sedatives administered to fish that may be consumed by humans, and the California Department of Fish and Wildlife (CDFW) approves methods of fish sedation or anesthesia occurring within the state. Until recently, the only FDA-approved sedative was tricaine methanesulfonate, known as MS-222. However, CDFW recently advised researchers that the use of this tried-and-true substance is no longer permitted for research specimens intended for immediate release - leaving many researchers in a search for alternatives.


Fisheries research isn't the only application for fish sedation: it's also used for the transport and processing of live fish for aquaculture and the aquarium trade to reduce stress and minimize fish mortality or injury. Sedated fish experience a decreased metabolic rate, so can be transported at higher densities to markets or for stocking purposes. Aquaculture operations often sedate fish prior to harvest, a practice referred to as "rested harvest," which minimizes stress-induced lactic acid buildup and consequently improves the color, appearance, texture and consistency of the food product (Bosworth et al. 2007). A variety of fish sedatives are known, and some natural products that are widely available, such as clove oil, are popular with aquarists. However, fisheries researchers and the aquaculture sector typically rely on commercial products specifically manufactured for the purpose of fish sedation or anesthesia.


Sedatives are subject to extensive testing before FDA approval for use in fish intended for consumption. While clove oil can be used in dental cement or food additives, neither clove oil nor any of its components are regarded as safe for use as a fish anesthetic until further tests prove conclusive. The FDA has approved the use of MS-222 for fish intended for consumption, with the stipulation of a 21-day withdrawal period before fish can be harvested and consumed. While such a withdrawal period is impractical for some management tasks (such as stocking purposes), research activities in California that involve species or specimens not subject to human consumption have typically relied on the use of MS-222 for sedation.


However, it's not easy to determine whether a fish encountered in the field may actually end up on someone's dinner plate. One might assume that the 21-day withdrawal period is not a concern for fishes that are illegal to harvest, and therefore consume, such as wild rainbow trout/steelhead in anadromous waters of the Central Valley, or Chinook salmon fry and juveniles. However, there are multiple accounts of anglers proudly delivering telemetry tags from protected fish to a local CDFW office - tags discovered while preparing their catch for the frying pan. Such incidents illustrate that even protected fish may occasionally be consumed.


The CDFW announced that the recent ban on MS-222 is intended to protect the health of "those that may unknowingly consume [MS-222] through capturing fish and wildlife for use as food." The only remaining alternative fish sedative for research that does not require additional approval is carbon dioxide, for which it is often difficult to determine, achieve, and maintain a proper dosage for fish sedation.This recent change in regulations has researchers throughout the state scrambling for other options to replace MS-222 and continue with their scheduled research activities. The FDA has granted authorization for the immediate release of fishes sedated with Auqi-S in field applications, though under strict stipulations including time-consuming and costly approval, registration, and detailed reporting. Although far from a quick and easy solution, we hope that this authorization is an important step towards finding an appropriate sedative that is safe for the specimen under study, the researchers that use it, and those who catch and eat protected fish.
Follow Us! Like us on Facebook Follow us on Twitter View our photos on flickr View our videos on YouTube
email list
Recent Blog Posts
Taking it portable
Our work often calls for quick thinking and adaptability. Last year, we ran into a situation where we  had to come up with an electrofishing boat in a hurry (see How to fabricate an electrofishing boat in 24 hours). Luckily, our master fabricators were able to modify one of our smaller boats with the necessary components to get the job done. Since we are always looking for innovative ways to be more efficient and flexible, we recently came up with a system that will help us be just that. Rather than dedicating a boat or two to electrofishing only, we wanted to have an easy way retrofit any of our boats with an electrofishing system. Our solution was to build a lightweight electrofishing deck that can attach to the bow of a boat and be ready for action without much setup time.
We fabricated our electrofishing deck out of lightweight aluminum to make it portable enough for two people to lift into place and limit the effect on boat performance. The platform is complete with pole-mounted anodes, diodes, lights, safety rails and a non-slip floor. Once the deck is in place, a generator and the heart of the system, a Smith-Root GPP electrofisher, are placed at the stern of the boat. Thanks to the creativity and innovation of our master fabricators, we can now quickly adapt any of our boats for electrofishing and get back out on the water in a hurry... Read more > 
IN THE NEWS: Recent stories you might have missed...
Drought leads to tough tradeoffs for California salmon 

While farms and cities struggle with low water supplies, California wildlife managers are struggling to protect the fish facing the same problem. State officials are trying to avoid some of the worst impacts on endangered salmon, but helping some fish could actually harm others. "I think everyone who works on salmon is concerned right now, looking at the drought unfolding," said Mara Rea of the National Marine Fisheries Service... Read more >

Drought blocking passages to sea for California coho salmon
Los Angeles Times  
By now, water would typically be ripping down Scott Creek, and months ago it should have burst through a berm of sand to provide fish passage between freshwater and the ocean. Instead, young coho salmon from this redwood and oak-shaded watershed near Santa Cruz last week were swirling around idly in a lagoon. There has been so little rain that sand has blocked the endangered fish from leaving for the ocean or swimming upstream to spawn.... Read more >
Stalking Puget Sound steelhead with science

The government scientist's pursuit of these anadromous trout has brought him to the deck of the Chasina, a research vessel that's motoring through choppy gray waters of southern Puget Sound near the Tacoma Narrows Bridge. He's here to lay the groundwork for an experiment that could explain why so few steelhead are completing their journey through Puget Sound and on to the Pacific Ocean. Since 2007, Puget Sound steelhead have been listed as threatened under the Endangered Species Act... Read more > 

Study examines recycling of Cowlitz summer steelhead   

The Columbian

Recycling of hatchery summer steelhead in the lower Cowlitz River presents minimal risk to wild fish in the system, a preliminary U.S. Geological Survey study says. "Intensive monitoring of the key spawning tributaries failed to detect a single fish during the spawning period,'' according to the executive summary of the research, done in 2012 and 2013. The Washington Department of Fish and Wildlife and Tacoma Power also participated in the research... Read more >  

59% of Marine Protected Areas are ineffective


Protecting large, isolated areas of no-take zones for over 10 years with strong enforcement is the key to effective Marine Protected Areas (MPAs), according to a letter published this week in Nature. However, 59% of all MPAs meet less than three of the five criteria, making them protected in name only. The authors look at 964 sites in 87 MPAs worldwide and identify which factors determine a successful MPA... Read more >