Friday, February 15, 2013

How Stressed is Your Goldfish?

 How Stressed is Your Goldfish? Taking a Closer Look at the Ornamental Aquarium Trade
By: Morgan Ivens-Duran

            A couple of weeks ago, my research lab came into possession of a beautiful blue beta fish that was left over from an experiment in an undergraduate Animal Behavior class. I was thrilled. My desk is positioned next to a previously empty fish tank that had been left behind by a previous generation of graduate students, and for months I had gazed upon this desolate, barren 25 cubic liter environment. That afternoon, I went to a local aquarium shop to pick out some companions for our new lab mascot.

Blue beta fish. Image from

            Years ago in my high school Honors Biology class, I had been given the responsibility of maintaining a fish tank and frequently visited a local aquarium shop to replace those that had fallen ill to some sort of disease or parasite. At the time, I hadn’t stopped to think much about where these small creatures had come from. Now, after years of educating myself about conservation issues and reading scientific literature about various anthropogenic impacts on the marine environments, as I looked around the small, brightly lit shop with tanks containing multitudes of brightly colored fishes, I stopped to think about what these fish might have gone through during their journey from their native reefs to the present moment.

Tropical coral reef. Image from

            Approximately 2,000 species and millions of individual organisms are sold each year in the ornamental fish trade, whose value is estimated at around $900 million US dollars. Sixty percent of these ornamental fish are destined for US aquarium owners, and while many individuals are now obtained from commercial production facilities, a significant portion is still sourced from the wild. The aquarium trade is comprised of roughly equal proportions of fresh and saltwater fish, the latter of which are primarily collected from coral reefs in tropical Southeast Asian countries such as Thailand, Indonesia, and Singapore. In recent years, there has been a shift from aquaria containing only ornamental fish to the creation of miniature reef ecosystems, which has dramatically increased the diversity of species and magnitude of the ornamental aquarium trade as aquarists now purchase live coral and invertebrates in addition to showy, ornamental fish. This dependence on coral reef ecosystems, which are already subject to a variety of other anthropogenic impacts, is both a blessing and a curse. While continued exploitation depletes local populations and harvesting practices are often destructive, these habitats represent a tangible economic resource that could spur conservation measures in ways that more abstract ecosystem services might not.
            While as a marine ecologist I find all of this fascinating, this blog is about organismal physiology, not marine conservation issues. So, having set the stage, lets get into some of the details of how the aquarium trade affects the organisms that pass through it every day. In particular, I want to discuss the physiological reasons underlying the high rates of mortality seen in the aquarium industry.
            In the 1950’s, up to 50% of the fish collected would die during collection, and on average an additional 30% would die at each step along the chain of custody. While mortality rates are no longer quite that high, a significant number of organisms still die along their journey from their native waters to your local pet store.
Diagram showing the typical chain of custody for fish in the aquarium trade, both wild-collected and farmed. From Livengood and Chapman (2008).

            Because of the immense scale of the aquarium trade and the difficulty of replicating travel conditions in a laboratory setting, pinning down the exact causes of this widespread mortality has been difficult. However, within the last decade or so findings from a variety of studies have begun to illuminate the complex combinations of stressors that result in the death of so many ornamental fish and associated creatures.
            Handling stress, poor water quality during shipment, and periodic severe stressors have all been shown to increase mortality of ornamental fish. Although the use of toxic chemicals such as cyanide in reef fish collection is declining, it has not yet disappeared. Exposure to cyanide for as little as 2 minutes has been shown to cause damage on a cellular level and impair physiological function due to extensive damage to tissues in the liver, kidney, spleen, and brain. The physical act of handling fish during collection can also increase stress. Reef fish often secrete a thin layer of mucus that provides an important buffer against osmotic stress. Even mild abrasions can disrupt that protective shield, increasing the sensitivity of the fish to the fluctuating water conditions that often follow. During transport, the water can oscillate between extremes of temperature, light exposure, and pH. Crowding not only limits mobility, but also causes both a rapid buildup of toxic nitrogenous wastes produced by the teeming masses of fish and decreases in the levels of dissolved oxygen. Unfortunately, well-intentioned attempts by fishers to change the aqueous environment of these fish can have deleterious consequences. Tlustly et al. (2005) followed a supply route of cardinal tetras (Paracherodon axelrodi) from the Rio Negro in Brazil to their final destination, the New England Aquarium in Boston, MA. They found that when the piabeiros added new water to the 10-liter casapas used to transport the tetras, the pressure of that fresh water hitting the fish was enough to stun or even kill them.

Cardinal tetra. Image from

            Since most fish in the aquarium trade suffer from poor water quality in addition to the occasional shock of the containing crate falling over or being dropped, is it any wonder that individuals from many species don’t survive the multi-day journey?
            Given the picture I’ve just painted above, it may seem that the odds are overwhelmingly against any given fish in the aquarium trade surviving the topsy-turvy voyage that is the global aquarium trade. However, some species seem to be more resistant to these types of stressors. One notable example is the pot-bellied seahorse (Hippocampus abdominalis).
Pot-bellied seahorse. Image from

            In mammals, stressful situations induce the release of corticosteroids. In invertebrates, the stress response involves the release of adrenaline from chromaffin cells in the kidney, which causes the breakdown of glycogen into glucose (a form of chemical energy) as well as an increase in heart rate, respiration rate, and the oxygen-carrying capacity of the blood. Collectively, these types of responses are known as the sympathetic nervous system, or in more colloquial terms, “the flight or fight response.” Wright et al. (2007) set out to see if this classic stress response was evident in the pot-bellied seahorse when exposed to common stressors in the aquarium trade such as handling and confinement. Surprisingly, it seems that the sedentary nature of this animal prevents the stress response seen in so many other ornamental aquarium species.
            However, this singular example does little to counteract the overwhelming magnitude of species that are ill-suited for inclusion the aquarium trade, at least in its current state of regulation. Although there are a variety of ongoing efforts by both organizations within and external to the aquarium industry pushing for stronger regulations, ultimately it is up to us as consumers to create the economic incentive for companies to combat the rampant mortality rates currently plaguing the industry.
Tropical coral reef. Image from    

            That afternoon, as I stood in that small shop, I am sorry to admit that I noticed the large tank of live coral, representing decades if not hundreds of years of growth in a far away tropical sea. I noticed the various wild-collected tropical fishes and prawns and anemones. But rather than voice my concerns, I picked out three brightly colored guppies and a few aquatic plants and went about my business. If there was a silver lining, it is that my experience that afternoon prompted me to research this topic in far more detail than I ever had before, and to write this blog post in the hopes that the next time we visit a shop to purchase a new addition for our tank, we will do so with our eyes pried open a little wider.


Livengood, E.J., and F.A. Chapman. 2008. The ornamental fish trade: An introduction with perspectives for responsible aquarium fish ownership. University of Florida IFAS Extension, (FA124). Fisheries and Aquatic Sciences.

Rhyne, A.L., M.F. Tlusty, P.J. Schofield, L. Kaufman, J.A. Morris, Jr., and A.W. Bruckner. 2012. Revealing the appetite of the marine aquarium fish trade: The volume and biodiversity of fish imported into the United States. PLoS One 7(5):1-9.

Rubec, P.J. and F.P. Cruz. 2005. Monitoring the chain of custody to reduce delayed mortality of net-caught fish in the aquarium trade. SPC Live Reef Fish Information Bulletin 13:13-23.

Schmit, C. and A. Kunzmann. 2005. Post-harvest mortality in the marine aquarium trade: A case study of an Indonesian export facility. SPC Live Reef Fish Information Bulletin 13:3-12.

Tlusty, M., S. Dowd, S. Weber, R. Cooper, N.L. Chao, and B. Whittaker. 2005. Shipping cardinal tetras from the Amazon- understanding stressors to decrease shipping mortality. Ornamental Fish International 48:21-23.

Wright, K.A., C.M.C. Woods, B.E. Gray, and P.M. Lokman. 2007. Recovery from acute, chronic and transport stress in the pot-bellied seahorse Hippocampus abdominalis. Journal of Fish Biology 70:1447-1457.

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