Meeting Abstract
Anti-predator defense is important for survival, especially for slow-moving benthic fishes who can’t outrun larger predators. In cottoid fishes, preopercular spines are caudally oriented defensive structures with one or more sharp branches. In this study we examined the ontogeny and performance of preopercular spine in the Great Sculpin (Myoxocephalus polyacanthocephalus), a bottom dwelling piscivore that can reach 80cm TL. We sampled 15 M. polyacanthocephalus from 3 to 27 cm (SL) and found that spines grew isometrically in both length and width. To test performance we measured the ease with which spines were able to penetrate a synthetic proxy of predator’s flesh. We used silicone rubber block and measured penetration force as the spines were inserted to 75 percent of spine length. Puncture force scaled negatively with length – as individuals get larger, their spines become more efficient at penetration. Another aspect of spine performance is resistance to breakage. We used finite elemental models of three M. polyacanthocephalus spines from three size bins (0-10 cm, 10-20 cm, 20-30 cm) to analyze Von Mises stress distribution and magnitude across a size gradient. We found that maximum Von Mises stress localized to the tips of the spines, and was higher in smaller spines than in larger spines, indicating that the spines of smaller fishes are more likely to break with a load proportional to their spine size. This may reflect a difference in predation pressure, with smaller fish relying on crypsis and larger ones on spines for defence.
