Counting Nemo: anemonefish Amphiprion ocellaris identify species by number of white bars.

The brilliant colors of coral reef fish have received much research attention. This is well exemplified by anemonefish, which have distinct white bar patterns and inhabit host anemones and defend them as a territory. The 28 described species have between 0 and 3 white bars present, which has been suggested to be important for species recognition. In the present study, we found that Amphiprion ocellaris (a species that displays three white bars) hatched and reared in aquaria, when faced with an intruder fish, attacked their own species more frequently than other species of intruding anemonefish. Additionally, we explicitly tested whether this species could distinguish models with different numbers of bars. For this, 120 individuals of A. ocellaris were presented with four different models (no bars, and 1, 2 and 3 bars) and we compared whether the frequency of aggressive behavior towards the model differed according to the number of bars. The frequency of aggressive behavior toward the 3-bar model was the same as against living A. ocellaris, and was higher than towards any of the other models. We conclude that A. ocellaris use the number of white bars as a cue to identify and attack only competitors that might use the same host. We considered this as an important behavior for efficient host defense.

Colour patterns influence symbiosis and competition in the anemonefish-host anemone symbiosis system.

Colour patterns in fish are often used as an important medium for communication. Anemonefish, characterized by specific patterns of white bars, inhabit host anemones and defend the area around an anemone as their territory. The host anemone is used not only by the anemonefish, but also by other fish species that use anemones as temporary shelters. Anemonefish may be able to identify potential competitors by their colour patterns. We first examined the colour patterns of fish using host anemones inhabited by Amphiprion ocellaris as shelter and compared them with the patterns of fish using surrounding scleractinian corals. There were no fish with bars sheltering in host anemones, although many fish with bars were found in surrounding corals. Next, two fish models, one with white bars and the other with white stripes on a black background, were presented to an A. ocellaris colony. The duration of aggressive behaviour towards the bar model was significantly longer than that towards the stripe model. We conclude that differences in aggressive behaviour by the anemonefish possibly select the colour patterns of cohabiting fish. This study indicates that colour patterns may influence not only intraspecific interactions but also interspecific interactions in coral reef ecosystems.

Large host anemones can be shelters of a diverse assemblage of fish species, not just anemonefish.

The mutualistic relationships between anemonefish (Amphiprion; Pomacentridae) and host sea anemones are well known, but host anemones are also used as shelter by damselfish (Pomacentridae), wrasses (Labridae) and cardinalfish (Apogonidae). The threespot dascyllus Dascyllus trimaculatus (Pomacentridae) is known to live on or near host anemones in their immature phase. Nonetheless, detailed studies on the use of host anemones by other fish species have not yet been conducted. To understand the factors that influence the use of host anemones by other fish species, this study investigated the fish biota around host anemones in the Ryukyu Archipelago. Other than Amphiprion spp. and D. trimaculatus, 10 additional species of fish (9 species of damselfish and 1 species of cardinalfish) were confirmed to temporarily use host anemones as shelter, and five species of wrasse including Labroides dimidiatus came to clean anemonefish. Logistic regression analyses (independent variable: presence or absence of other species of fish; dependent variables: anemonefish aggressiveness, size of host anemone, number of D. trimaculatus) indicated that the size of host anemones is important for the presence of fish, both in species using the anemone as temporary shelter and in cleaner species. Large host anemones can provide shelter and food resources for other species of coral reef fish as well as for anemonefish.

Variation on a theme: pigmentation variants and mutants of anemonefish.

Pigmentation patterning systems are of great interest to understand how changes in developmental mechanisms can lead to a wide variety of patterns. These patterns are often conspicuous, but their origins remain elusive for many marine fish species. Dismantling a biological system allows a better understanding of the required components and the deciphering of how such complex systems are established and function. Valuable information can be obtained from detailed analyses and comparisons of pigmentation patterns of mutants and/or variants from normal patterns. Anemonefishes have been popular marine fish in aquaculture for many years, which has led to the isolation of several mutant lines, and in particular color alterations, that have become very popular in the pet trade. Additionally, scattered information about naturally occurring aberrant anemonefish is available on various websites and image platforms. In this review, the available information on anemonefish color pattern alterations has been gathered and compiled in order to characterize and compare different mutations. With the global picture of anemonefish mutants and variants emerging from this, such as presence or absence of certain phenotypes, information on the patterning system itself can be gained.