One of the distinguishing features of sticklebacks is that instead of having pelvic and dorsal fins, they have serrated bony spines that the fish can lock into place(more on the locking in a later entry).
Why would evolution result in a lineage of fishes that has spines instead of fins? The classic explanation is that spines make sticklebacks a painful meal; predators will avoid eating sticklebacks if other food is available.
In 1956, Hoogland et al tested whether stickleback spines were an effective defense against larger fish. The paper itself is 33 pages, with multiple experiments – for today’s entry, I’m going to concentrate on only two of these.
In the first experiment, pike were presented with three different types of fish: 12 threespine sticklebacks, 12 ninespine sticklebacks, and 12 carplike fish lacking spines. At first, the pike went after sticklebacks, with decidedly ouch-inducing results:
After eating one stickleback of each type, the pike focused exclusively on the fish without spines, eating all 12 of them in 5 days. Once all of these were gone, sticklebacks started disappearing, but at a much slower pace, with ninespine stickleback eaten faster than threespines. It’s difficult to conclude anything too comprehensively from this, as the authors didn’t do much in the way of replication, but it does suggest that fish predators prefer nonspined prey.
Then, the authors tried the obvious experiment – if threespine stickleback have spines that make it difficult for predators to eat them, what happens if the spines are removed? Once the spines were removed from a stickleback, predators stopped spitting them out and treated them similarly to the carplike fish.
Provided one is willing to overlook the paper’s archaic methodology and lack of rigorous statistical methods(and it is from the 1950s, remember), spines appear to decrease the deliciousness of stickleback.
Perhaps that’s why sticklebacks have never really taken off as a cuisine…
R. Hoogland, D. Morris and N. Tinbergen (1956). The Spines of Sticklebacks (Gasterosteus and Pygosteus) as Means of Defence against Predators (Perca and Esox) Behaviour, 10 (3), 205-236 DOI: 10.2307/4532857