Seeing pairs of birds or mammals that cooperate or help each other out when they are feeding is far from uncommon, and it is in fact a key benefit of forming a monogamous pair. This behavior has been documented in many different species with a different degree of monogamy, but has never been seen in any non-mammal or non-bird until very recently.
A rabbitfish pair. Image by T. Cooper, posted with the Creative Commons Attribution 3.0 Unported license.
A research team from ARC Centre of Excellence for Coral Reef Studies at James Cook University studied rabbitfishes (Genus Siganus), a genus that consists of about 28 different species. They are all found in the Indo-Pacific ocean, and form pairs for breeding and foraging. Parrotfishes eat benthic algae in the wild, but some species have also been observed to be eating prawns, fishing bait, comb jellies and jellyfish, so they are believed to be opportunistic omnivores that will eat anything that can fit in their mouths.
The parrotfish are pretty popular to keep as pets in fish tanks, but they are easily frightened, and will use their venomous spines to defend themselves if they feel threatened, so it’s not really encouraged to keep them. The poison will not kill a grown adult, but it is very painful, and some people have compared it to being stung by a lionfish (Genus Pterois)!
Anyway, I want to take a closer look at how these parrotfishes exhibit reciprocal cooperation during foraging like I mentioned in the title, but first we need to understand what exactly that is.
A school of parrotfish. Image by Vincent C. Chen, posted with the Creative Commons Attribution-Share Alike 4.0 International license.
What is reciprocal cooperation?
Reciprocal cooperation is when one organism temporarily reduces their own fitness to improve the fitness of other organism. That was a pretty heavy biological definition, so let’s rephrase it to when one individual reduces their own chance of survival in order to help the other individual improve theirs. As said, there are many examples of this in the mammal and bird communities, such as when one individual is sharing food, or pretty much anytime someone helps someone else without an obvious advantage to the helper.
The thing about reciprocal cooperation is that it is based upon the expectation that the favor will be returned at some point. It makes no sense to share your food if you don’t expect the other organism to share their food at one point, so it works on a “tit for tat” strategy.
Image by Citron / CC-BY-SA-3.0.
While this might sound pretty easy and internalized to us humans, this survival strategy is thought to require complex social and cognitive skills. For this reason scientists have assumed that it would simply be impossible for any species of fish to exhibit this behavior.
The scientists found behavior of reciprocal foraging cooperation in the rabbitfish
Let’s return to the research by ARC Centre of Excellence for Coral Reef Studies. Their study found clear signs that the parrotfish pairs would exhibit reciprocal cooperation when foraging for algae. This was observed when pairs foraged together, and one member of the pair would assume a vigilant position where it was on the lookout for intruders, while the other member found focus on eating algae. After a little while the members would change positions, suggesting that they had a balanced distribution of foraging activity.
When the one member is on the lookout for predators while the other is foraging, it is increasing its chances of being eaten, since it would be better off to go hide while the other member ate. However, the study also found that the member who was foraging had on average better success compared to individual rabbitfish who foraged alone. This further suggests that the cost of being on the lookout for your partner is outweighed by the gain from a better forage.
All in all, there is strong evidence that these fish exhibit reciprocal cooperation, even though we did not expect fish to be able to do this!
Image is Public Domain.
Could fish have more social behavior then we expect?
The commonly accepted notion of the fish have always been that they are pretty straightforward creatures that fend for themselves, and don’t really exhibit complex social behaviors. However, studies like this could begin to change how we look at the fish in general, and it will be exciting to see if we can find even more complex social behavior in fish from now on.
Thanks for reading
Thanks for reading about how the rabbitfish exhibit reciprocal cooperation. I hope you enjoyed the post, and please let me know if you have any questions. The link to the study is further up in the text. Also keep in mind that the study itself is a few years old, so it’s not brand new like most studies that I write about.
And to end, let’s have a bonus grammar funfact: You might notice that I write rabbitfishes, but commonly refer to multiple fish as fish, not fishes (which is how it is supposed to be). When using the word fishes we refer to multiple species of a fish genus, while the word fish can be used to refer to several fish of the same species. Alright, enough grammar fun for now.
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