Coral reefs are home to more than 35,000 marine species. These species range from simple plankton all the way up to complex reef sharks. One little fish that I have found to be extremely interesting is the Longfin Damselfish. Every living organism in the world has a common name and a scientific name. The scientific name of Longfin Damselfish is Stegates diencaeus in the family Pomacentridae.

Adult Longfin Damselfish reach a length of 12.5 cm when they become full grown. Adults are commonly a blackish-grey color and their snout and nape of the neck have a yellowish-brown tint. On their anal fin, you can see a bright blue coloring just on the outer most part of their fin. Their head is generally small and contains a small row of sharp front teeth. Their dorsal fin is singular and continuous with 12 spines and 14-17 rays. Their anal fin also contains rays and 2 spines. Just like humans, juveniles and adults look much different. When Longfin Damselfish are younger, their bodies are bright yellow. There are two purple-blue stripes that start at their head and continue all the way back to their anal fins. Once the stripe gets to the anal fin, it ends with a large black dot just at the base of their anal fin.

Longfin Damselfish juvenile by zsispeo via Flickr
Longfin Damselfish by zsispeo via Flickr 

Longfin Damselfish can be found in the Atlantic Ocean, mainly in southern Florida, Bahamas, Mexico and the Carribean. They like to make their homes in coral and rocky reefs. They are a very territorial species and will spend most of their lives by themselves or with their mate. It is unknown at what points during the year Longfin Damselfish mate, but, we do know that they always spawn at dawn. When the mating season begins, the male and female engage in a “mating dance” with rapid swimming and fin movements. During this time, the males will turn a shade or two darker and some display white blotches. Once the female picks her mate, she lays a ton of sticky eggs that stick to the nest. The male then comes and fertilizes the eggs. After fertilization, the male will protect the eggs until they are hatched. This usually takes roughly 2-3 days.

Longfin Damselfish consume mostly algae, plankton, and benthic invertebrates. This puts them in the category of secondary feeders. The only natural known predator that they have is the Lion Fish. While this predator is an invasive species with no known predators of their own, the Longfin Damselfish species is nowhere near endangered. Longfin Damselfish are also caught for the aquarium trade. Fishermen have to use nets and traps to catch the Longfin damselfish. They are known as nibblers so they can not be caught with hook and line. While they are caught by humans for sale, it does not appear to be globally affecting their populations.


The information in this chapter is thanks to content contributions from Morgan Tupper


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A Student's Guide to Tropical Marine Biology Copyright © by by Keene State College Students, BIO 381 Tropical Marine Biology is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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