Britannica
Sources used in this answer
What roles do the dorsal and anal fins play in swimming?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
fish
Diodon hystrix is a species of porcupine fish. These fishes are short and broad-bodied, with large eyes and spines covering their skin. Like puffer fishes, they inflate their bodies when threatened.
The dorsal and anal fins are primarily responsible for stabilizing a fish during movement. Specifically, the dorsal fin, often working in conjunction with a ventral fin, acts to prevent yawing—the lateral seesawing or side-to-side instability of the body. To be most effective in this role, the surface area of these fins is typically positioned behind the fish's centre of gravity.1
While these fins are generally used for stabilization, their roles can shift in species with specialized body forms. For example, in certain groups like knifefishes and electric eels, the dorsal fin may be lost entirely, and the anal fin becomes a primary organ for propulsion, enabling slow forward and backward movements through undulations of its length.2