The Giant Kelpfish (Heterostichus rostratus) is a 10–24 inch species of marine fish, and the largest member of the Clinidae family.

To allow it to blend in, the giant kelpfish has three morphs: red, brown and green, often with melanistic barring or striping patterns depending on sex, developmental stage, and habitat.

It may be confused with the Striped Kelpfish (Gibbonsia metzi) which are similar-bodied but are more prominently barred, have a rounded tail and a subterminal mouth.

It inhabits rocky areas with dense canopies of microalga, giant kelp and other large seaweeds.

Juveniles have been observed to utilize the upper portions of microalga while the older individuals gather near the base of the plant.

[7] They prefer to live near the surface to moderately deep waters due to the abundance of sunlight and in turn, dense vegetation for their nests and protection.

The Giant Kelpfish is oviparous, meaning they lay eggs, as opposed to some other members of the Clinidae family that are viviparous, and which rear live young.

There may be a high mortality rate during this time while they are growing exponentially and are adapting to capturing larger prey and fulfilling their caloric intake requirements.

It has also been observed that the male exhibits a nuptial melanistic striping pattern in which they alter their coloration for the purpose of sexual signaling.

Their elongated, flattened bodies and independently controlled pectoral fins allow them to make precise maneuvers through dense vegetation to evade predators as well as to ambush prey.

A potential threat that may arise is loss of habitat due to climate change and its resulting consequences such as ocean acidification and pollution, as well as destruction and/or massive die-offs of kelp forests.