UNDER THE SEA

 Hello ladies and gents this is the Viking telling you that today we are talking about

DAMSELFISH

Damselfishes comprise the family Pomacentridae except those of the genera Amphiprion and Premnas, which are the anemonefishes. The largest can grow up to 36 cm (14 in) long, but most species are much smaller. While most are marine, a few species inhabit the lower stretches of rivers in fresh water. Most damselfish species have bright colors or strongly contrasting patterns.

Habitat

Many species live in tropical rocky or coral reefs, and many of those are kept as marine aquarium pets. Their diets include small crustaceans, plankton, and algae. However, a few live in fresh and brackish waters, such as the freshwater damselfish, or in warm temperate climates, such as the large orange Garibaldi, which inhabits the coast of southern California and the Pacific Mexican coast.

Foraging

The domino damselfish D. albisella spends the majority (greater than 85%) of its daytime hours foraging. Larger individuals typically forage higher in a water column than do smaller ones. Damselfish of all sizes feed primarily on caridea and copepods. Males have relatively smaller stomach sizes during spawning season compared to females due to the allocation of resources for courtship and the guarding of nests. 

When current speeds are low, the damselfish forages higher in a water column where the flux of plankton is greater and they have a larger food source. As current speeds increase, it forages closer to the bottom of the column. Feeding rates tend to be higher when currents are faster. Smaller fishes forage closer to their substrates than do larger ones, possibly in response to predation pressures.

Territoriality

The threespot damselfish S. planifrons is very territorial and defends its food and reproductive sites vigorously from intruders. Females leave their territories temporarily during spawning in order to deposit their eggs in male territories. This increased mobility subjects them to greater risks of predation, and females typically exhibit higher turnover rates than males do. Male damselfish defend their clutches until the larvae hatch. They do so by continuously swimming in a circular pattern around their nests. Males compete against each other for reproductive territorial space. 

Smaller and less aggressive individuals are often relegated to secondary or suboptimal habitats and therefore exhibit lesser reproductive success. Some are excluded from establishing territories altogether and usually exist as a floating population. These fish do not take part in breeding and are at the greatest risk of predation. However, they may occupy territories that have been vacated whenever the opportunity arises.

The dusky damselfish S. adustus spends the majority of its life within a territory that is only about 0.6 m2 in area. These territories provide them with hiding spots, dietary needs, and spawning sites. Individuals in suboptimal territories frequently attempt to relocate, and so those in optimal habitats must constantly monitor territorial occupancy. Territorial aggression is often proportional to territory quality. 

Movements outside of territorial borders, called forays, are common and may span distances of sixteen meters or more. Three types of forays exist. The shortest-distance ones are involved in foraging. Longer forays usually involve courtship activity and mating. Non-feeding and non-reproductive forays are associated with territorial reoccupation. The blue velvet damsel fish is very aggressive against other male blue velvet damsels.

Courtship

In the species S. partitus, females do not choose to mate with males based on size. Even though large male size can be advantageous in defending nests and eggs against conspecifics among many animals, nest intrusions are not observed in this damselfish species. Females also do not choose their mates based upon the brood sizes of the males. 

In spite of the increased male parental care, brood size does not affect egg survival, as eggs are typically taken during the night when the males are not defending their nests. Rather, female choice of mates is dependent on male courtship rate. Males signal their parental quality by the vigor of their courtship displays, and females mate preferentially with vigorously courting males.

Male damselfish perform a courtship behavior called the signal jump, in which they rise in a water column and then rapidly swim back downward. The signal jump involves large amounts of rapid swimming, and females choose mates based on the vigor with which males do so. Females determine the male courtship rates using sounds that are produced during signal jumps. As the male damselfish swims down the water column, it creates a pulsed sound. Male courtship varies in the number and rates of those pulses.

In the beaugregory damselfish S. leucostictus males spend more time courting females that are larger in size. Female size is significantly correlated with ovary weight, and males intensify their courtship rituals for the more fecund females. Research has shown that males that mate with larger females do indeed receive and hatch greater numbers of eggs.

Mating

Male bicolor damselfish, E. partitus, exhibit polygamy, often courting multiple females simultaneously. Among this species, evolutionary selection favors those males that begin mating as soon as possible during spawning seasons even if the most favorable egg clutches are spawned at later times. Females often choose which males to mate with depending on the males’ territory quality. Shelter sites are essential for the bicolor damselfish in avoiding predation, and females may evaluate the suitability of these sites at a male territory before depositing their eggs