20 September 2013

Fish Eyespots

Welcome back. Do you have tropical fish as pets? Although Godzilla, my wife’s algae-eating pleco, was unquestionably the most engrossing pet I’ve ever encountered and left notes about to our pet sitter (Time for Non-Furry Pets), I’m not a big fan of fish as pets. Most are beautiful, relaxing and boring.

Plus, when I was an unwitting grad student, I had the experience of minding two goldfish for a weekend for a neighbor’s young kids. The fish expressed their resentment at being left behind by trying to leap out of the bowl then dying. (Who knew fish weren’t fond of chlorinated water from the tap?) Goldfish are hard to match on short notice.

Anyway, I think tropical fish are magnificent in the wild or even in appropriately huge, balanced aquariums. Occasionally I also find research on tropical fish that I think is interesting. A recent study from Australia’s James Cook University, with contributions from the University of Saskatchewan, Canada, is downright intriguing.

Eyespot Research

I’m sure you’ve seen butterflies or moths that have eyespots, those eye-like markings on their wings. Eyespots can be found throughout the animal kingdom--mammals, amphibians, reptiles, insects and even fish. 

Ambon damselfish; note eyespot
on dorsal fin, near tail. (Photo from
Indonesian Biodiversity Research
Center website, www.ibrc-bali.org/)

This latest effort to understand the significance of eyespots experimented with juvenile Ambon damselfish, Pomacentrus amboinensis, which usually lose the eyespots on their dorsal fin as they mature.

The researchers released test damselfish into a tank where the fish could see and smell--but not be attacked by--predatory fish, while control damselfish were either isolated from other fish or exposed to non-predatory herbivores.

Predator-Induced Changes

Compared to the control fish, after only six weeks, the test damselfish grew deeper (taller) bodies--growing too big to get jaws around is a common prey response; they adopted more conservative, less active behaviors (you won’t notice me); and what is thought to be a new finding, they developed larger eyespots accompanied by stunted growth of their real eyes.

The investigators postulated that having a larger eyespot near the tail and smaller eyes on the head would confuse a predator about the damselfish’s direction of escape in addition to producing a less catastrophic result if the eyespot rather than the head were attacked.

And that’s what seemed to occur when the control and test damselfish were released into a natural environment. Some 40% to 50% of the control fish became fish dinner within 48 hours; yet nearly 90% of the test fish were still swimming around after 96 hours.

Wrap Up

Depending on your family status or taste in cinema, you may be wondering if there is any relationship between damselfish and the star of the movie, Finding Nemo. I’ve checked the entertainment sources and can report that, although the fish who played Nemo is a clownfish or anemonefish, he’s in the same family, Pomacentridae. Small world isn’t it? Thanks for stopping by.


- Research report on Nature website: www.nature.com/srep/2013/130725/srep02259/full/srep02259.html
- Examples of articles on the work; these from ScienceDaily and Discovery:
- Wikipedia write up on eyespots:
- Background on damselfish:

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