Posted on August 17, 2011 - by

For Fish, Age is Not Just a Number

Image: Flickr/nhankamer

Today’s guest blog post is brought to you by FishWise, a non-profit sustainable seafood consultancy that helps seafood businesses improve the sustainability of their seafood offerings.

Yes, all aquatic animals have birthdays. Some live for a matter of days or weeks, and others can live forever. (Yes, really.)

Although we can’t ask a fish its age (it’s simply impolite), there are ways we can determine the length of time that an individual fish has been alive. One popular method for aging fish involves analyzing bones in their heads called otoliths (“oto” meaning ear and “lith” meaning stone). When an otolith is removed from a fish, sectioned into thin slices and viewed through a microscope, it reveals a pattern of light and dark concentric rings. The darker, denser rings are often formed in the winter when growth is slow and in the warmer months, when a fish is growing more quickly, a clearer ring is formed. A pair of rings is called an “annuli” and is similar to the rings found in trees. Count the annuli and you can determine a fish’s age.

So what does this have to do with the seafood you buy and eat? Often, slow-growing fish take a long time to reach reproductive age, which leads to a greater risk of that fish being caught, or dying of natural causes, before it has a chance to reproduce. Consider the orange roughy, which takes around 30 years to reach sexual maturity. Whenever you take a fish that is younger than that out of the water, that fish has not had a chance to reproduce, which in turn affects the abundance and diversity of the next generation. Additionally, you run the risk of negatively affecting other animals in the food chain.

This would all be easier to swallow if fisherman were catching a responsible amount of orange roughy, taking into account the number of fish in each year class becoming sexually mature and selectively catching only those individuals. Unfortunately, this is not the case, and instead we are seeing fewer, younger and smaller orange roughy reach our plates.

There are a number of species that are characterized by a very high growth rate and abundance, Pacific sardines being an excellent example. Most sardine fisheries are considered a “Super Green” option by the Monterey Bay Aquarium due to these biological factors and because they are generally well-managed and recognized for their low levels of bycatch and clean fishing techniques. Choices that are similarly sustainable are handline-caught mahi mahi from the U.S. Atlantic and U.S. farmed crawfish.

We don’t suggest you memorize the longevity of all of your favorite seafood; scientists have done that for you. Rankings systems such as that by the Monterey Bay Aquarium Seafood Watch program take longevity and reproduction rates into account, so shop for seafood only on the green and yellow lists and you’re assured they’ll be around for you to eat well into your twilight years.

FishWise is a non-profit sustainable seafood consultancy that helps seafood businesses improve the sustainability of their seafood offerings through environmentally responsible business practices, such as policy development, employee training, sourcing assistance and point of sale information. This approach empowers consumer to make environmentally informed choices when purchasing seafood.

To learn more about sustainable seafood, visit or sign up for their mailing list.



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