Marine Animal Encyclopedia
Threespot Damselfish Stegastes planifrons
Species ID: P.SPb
Description: Small oval-shaped fish with a gently sloping forehead and rounded fins. Adults are ellowish-brown to dark brown and are characterized by a yellow crescent over the eye and dark spots at the base of each pectoral fin as well as straddling the tail. Sexes appear similar. Juveniles are bright yellow with one spot more than adults found at the top rear on each side of the body
Maximum Size: 13 cm (5 in)
Longevity: Up to 19 years
Status: Not currently on the IUCN endangered species list
Threespot Damselfish & People: Not fished for commercial or subsistence fisheries, and uncommon in the aquarium trade due to its aggressiveness
Geographical Range: Very common on coral reefs throughout the Caribbean
Coral Reef Zone: Found in virtually every coral reef zone – shore, back reef, reef flat, fore reef and drop-off zones
Favourite Habitat: Commonly seen on algae covered rock or coral rubble. Its preferred microhabitat is among the protective branches of staghorn coral (Acropora cervicornis) common in the back reef and fore reef zones
Depth: 1 – 30 m (3 – 100 ft)
A Day in The Life
Dawn: Spawning occurs within male territories just after sunrise
Day: Individuals feed, tend their algal gardens, and defend their territory
Dusk: Feeding and territorial activities are reduced and fish seek shelter for the night
Night: Fish hide in caves or within the branches of corals
Who Eats Who?
The threespot damselfish is a herbivore, feeding mainly on the algae that it cultivates as well as on the tiny organisms called epiphytes that grow on the algae. Despite its aggressiveness, the threespot damselfish has little in the way of protection against predation. It is eaten by a wide range of reef predators including grouper and jacks.
Scuba Diver & Snorkeler Best Practices
Refrain from feeding marine life. Coral reef organisms should never be fed. Although this may seem like a harmless practice that allows you to get close to your favourite organisms, it actually disturbs normal feeding patterns and diets. Scientists have documented turtles being fed bread, dog food and even cheese—none of these foods are found naturally in the marine environment, and they can cause untold stress to the organisms that consume them. Conditioning wild animals to become comfortable with hand-feeding by humans alters their behaviour and makes them more vulnerable to capture, which directly affect their survival—this is particularly a concern for endangered sea turtles.
These fish are unafraid and may even boldly attack intruders many times their size, including divers and snorkelers, although their bite only feels like a pinch.
Threespot damsels are herbivores that feed actively during the day. These damselfish are commonly seen inhabiting areas of bare rock, coral rubble, or thickets of staghorn coral (Acropora cervicornis), where they diligently culture algal gardens on bare rock or patches of dead coral. In order to expand its garden, a damselfish will often bite at living coral to kill it and allow their algae garden to spread over the coral’s bare skeleton, which is normally protected by mucus while alive. Corals often attempt to grow up around these tiny bite-marks, leading to tall, white tube-like growth formations known as “damselfish chimneys”.
Observe, record & share:
O P.SPb-101 – Algae lawn: Observe the patch of algae that the damselfish feeds on, cares for and defends
O P.SPb-102 – Damselfish chimneys: On staghorn coral colonies inhabited by threespot damselfish, you may notice the presence of pale, tube-like growths as the coral attempts to grow around the wounds inflicted by biting damselfish
Attack & Defense Behaviour
Threespot damselfish are fiercely territorial and will even defend their territories against intruders many times their own size. Threespot damselfish repel intruders from their territories with intimidating fin displays, headstand postures, chasing, biting, and sometimes even intimidating clicking and popping sounds. In the case of urchin intruders, who compete for algae, these damselfish will even pick them up by the spines and physically carry them away. Only the largest and fiercest individuals in a colony acquire prime real-estate in the well-protected centre of a staghorn coral thicket; and threespot damselfish size therefore tends to decrease as one moves from the centre towards the outskirts of a particular coral colony.
Observe, record & share:
O P.SPb-201 – Territorial dispute: Threespot damselfish repel intruders using fin displays, chasing and biting
O P.SPb-202 – Headstand: Damselfish facing a threat tilt their body towards the sea floor
O P.SPb-203 – Size distribution: On a coral colony, the largest individuals are in the centre and the smallest near the edges
O P.SPb-204 – Ejecting urchins: Threespot damselfish pick urchins up by the spines and carry them out of their territory
At dawn, ripe females that are ready to spawn leave their territory to find males with a suitable nest. Females and males may initiate spawning in slightly different ways. Females that are very motivated to spawn approach males with their back and belly paled to a light brown. Males may also initiate spawning by adopting a colour pattern where their back pales to white and the spots on their body darken, during which they adopt an exaggerated swimming style and make clicking sounds by vibrating their swim bladder. Once a couple forms, the males indicate the site of their nest by swimming to and from it, and then swimming vertical loops in a behaviour known as a “signal jump”. Females approach the nest and lay their eggs, while the males follow close behind to fertilize them. The male cleans and aggressively defends the eggs in his nest until they hatch. Spawning occurs just after dawn year round, with peaks in the winter months and in the days following a full moon. These fish do not undergo sex change during reproductive development.
Observe, record & share:
O P.SPb-301 – Eggs and egg care: Males care for the eggs by fanning them with the pectoral fins and picking out dead eggs and detritus
O P.SPb-302 – Nest guarding: Males caring for eggs will aggressively chase away intruders
O P.SPb-303 – Male courtship initiation and colours: Back of male pales to white and body spots darken, while adopting an exaggerated swimming style and making clicking sounds
O P.SPb-304 – Female courtship initiation and colours: Females approach males with back and belly paled to a light brown
O P.SPb-305 – Signal jump: Males dart to and from the nest site and make “signal jumps” to indicate where the female should lay her eggs
O P.SPb-306 – Spawning: The female lays her eggs and the male fertilizes them
Social structure: Threespot damselfish that share a coral colony with others live within the confines of a rigid social structure, where the biggest and strongest male is able to occupy the best territory in the well-protected centre of the coral. Smaller males and females must make do with territories in the outer fringes of the colony, which are much more exposed and thus vulnerable to intruders and predators. You may also notice damselfish chimneys that appear as very small, white tubular growths where the fish bite coral to kill it and allow the algae that they feed on to grow over the exposed skeleton.
Did You Know?
• Freshly laid threespot damselfish eggs are yellow and as they develop they darken to green just before hatching, roughly one week after being laid. Use this tip to try and gauge the age of egg patches you observe in the water.
• Like many other damselfish, this species may make popping or clicking sounds, produced by vibrating the swim bladder. However, these sounds are typically faint, low-pitched, and difficult for divers to hear.
What to do?
Share your observations today!: Discover your species of interest, observe its behaviour, and share your pictures and videos with friends and coral reef enthusiasts around the world! Upload media to the web, tagged with species common name (ex.: trumpetfish) and species ID code (ex.: A.AM) or species behaviour code (ex.: A.AM-101)