It’s a small world if you’re a miniature fish

By Stephanie Lefebvre, EEB

From elephants to ants, walruses to weevils, animals vary hugely in size. But how an animal’s size influences its life isn’t well understood.  For example, how have some of the world’s smallest fish adapted to life in miniature? It is a question that has hooked one fish biologist at the University of Toronto. Evolutionary biologist Sarah Steele, along with her colleagues at the Royal Ontario Museum (ROM), is interested in looking at how being only a few centimetres long influences what these fish eat, where and how long they live, and how they raise their young.  To investigate, Steele focused on fish from the Amazon. The rivers in this region have some of the smallest fish on the planet, like the Staecks dwarf cichlid (Apistrogramma staecki), which reaches only 2.1cm.

Steele found that closely related Neotropical cichlids fish aren’t necessarily similar in body size, nor live similar lifestyles. Steele explains that this could be because closely related fish evolved to be very different sizes because they find themselves in different environments.  For example, if you find yourself in the presence of much bigger fish,  being small allows you access to habitats the larger fish just can’t get at. “This could explain why we see both small and large fish in the same place; they can live together because they aren’t fighting for the same things,” says Steele.  “It’s interesting to try and piece together their story – we’ve got closely related fish doing very different things ecologically, but we still don’t know how it happened,” she adds.