Anemonefish Species Research Articles

Undisturbed swimming behaviour and nocturnal activity of coral reef fish larvae

Larval dispersal is shaped by the interaction between oceanographic processes and larval behaviour. To evaluate the potential impact of larval behaviour on this process, we quantified the undisturbed swimming speeds and nocturnal swimming activity of 5 reef fish species throughout their larval phase. We used video techniques to obtain undisturbed observations of swimming behaviour in captive bred larvae. The results conclusively demonstrate that larvae maintain relatively high swimming speeds throughout development. Speeds were consistent among 3 anemonefish species (Amphiprioninae; Amphiprion melanopus, A. percula and Premnas biaculeatus), which swam an average of 3.9 and a maximum of 8.4 body lengths (bl) s-1. However, differences may exist among taxa in the undisturbed swimming speeds of larvae. Highest speeds were recorded in the damselfish Pomacentrus amboinensis (Pomacentridae) and the slowest speeds in the cardinalfish Sphaeramia nematoptera (Apogonidae). The results support short-duration experimental and in situ evidence of high sustained swimming speeds. However, it is striking that larvae routinely swim at such speeds without external stimuli. The proportion of time larvae spent swimming at night increased rapidly towards the end of the larval phase in all 5 species examined. In addition, the undisturbed swimming speeds of larvae were significantly greater at night than during the day. Patterns of nocturnal activity appear to relate to the active nocturnal settlement behaviour of larvae. The pattern of swimming, and speeds achieved, suggest that an active behavioural mechanism for self-recruitment is well within the capabilities of the reef fish larvae examined.

Coexistence of nine anemonefish species: differential host and habitat utilization, size and recruitment

The region of Madang, Papua New Guinea, has the highest reported species diversity of both anemonefishes (nine species) and their host anemones (ten species). To determine which factors may allow so many anemonefish species to coexist at this location, we studied their patterns of distribution, abundance, and recruitment. Population surveys at three replicate reef sites within four zones situated at varying distances from the mainland (nearshore, mid-lagoon, outer barrier, and offshore) indicated that each species of host anemone and anemonefish lived within a particular range of zones. Each species of anemonefish lived primarily with one species of host. Anemonefish species that lived with the same host species usually had different distribution patterns among zones (e.g., Amphiprion percula occupied Heteractis magnifica in nearshore zones, while A. perideraion occupied H. magnifica in offshore zones). Monitoring of natural populations showed that there were few changes (losses or recruitment) in the number or species of fishes associated with each individual anemone over periods ranging from 3 to 9 months. Recruitment was monitored on anemones with and without residents (resident fishes were removed) within each of three zones (nearshore, mid-lagoon, outer barrier). Significantly more anemonefishes recruited to anemones without resident fishes than to anemones with resident fishes. Each anemonefish species recruited to particular host species and zones. The distribution and abundance of the recruits of each fish species among zones were positively correlated with the distribution and abundance of resident fishes in the benthic habitat. This suggests that the spatial patterns of recruitment among zones strongly determined the distribution and abundance patterns of the benthic populations, and they were not the result of post-recruitment mortality or movement. Coexistence of the nine anemonefish species on the limited anemone resource was considered possible because of niche differentiation (i.e., differences in host and habitat utilization among zones), and the ability of two small species (i.e., Amphiprion sandaracinos and A. leucokranos) to cohabit individual anemones with other anemonefish species.

Experimental evaluation of the roles of habitat selection and interspecific competition in determining patterns of host use by two anemonefishes

We examined the roles of interspecific competition and habitat preference in determining the distribution of 2 anemonefish species, Premnas biaculeatus and Amphiprion melanopus, among the 2 morphs of the anemone Entacmaea quadricolour. This anemone species has a solitary morph which is usually occupied by a single pair of P. biaculeatus and a colonial morph which is usually occupied by large social groups of A. melanopus. The possibility that interspecific competition, and/or preference of adults of each species of fish for the anemone morph it usually occupies, determines this distribution was tested using aquarium based experiments. Adults of one species, A. melanopus, displayed a preference for the anemone morph it usually occupies in the field, but P. biaculeatus did not. Instead, P. biaculeatus pairs tended to associate closely, always occupying the same anemone regardless of the morph chosen. While interspecific competition limited fish abundance within anemones, competitive interactions could not explain the distribution of fish species among anemone morphs. That is, neither fish species displaced the other more often on the anemone morph it usually occupies in the field. While juvenile P. biaculeatus exhibit some preference for solitary morphs and A. melanopus appear to prefer colonial morphs, juvenile distributions cannot fully explain the distribution of adults. Instead, we suggest that adult distributions are explained by a combination of juvenile habitat preferences, adult-juvenile interactions and constraints imposed by the contrasting social systems of the 2 species.

Ontogenetic and interspecific variation in the protection of anemonefishes from sea anemones

Anemonefishes are well known for their ability to live unharmed among the stinging tentacles of sea anemones. This study examined whether there is ontogenetic and interspecific variation in the protection of anemonefishes from being stung by symbiotic anemones. Ontogenetic variation in protection was studied by determining if the tentacles of anemones would adhere to the eggs, larvae (0–5 days old), and recently metamorphosed anemonefish juveniles (7–14 days old). Interspecific variation in protection was examined by forcing juveniles of 10 species of anemonefishes to contact the tentacles of up to 9 anemone species. The tentacle adhesive forces of the anemone species were also measured. The eggs of anemonefishes were protected from all species of symbiotic anemones tested. Larval fishes were captured and killed by anemones, but recently metamorphosed juvenile fishes were protected from certain host species. Thus, the anemonefishes developed some form of protection during metamorphosis from a pelagic larva to a benthic juvenile. The juveniles of only one anemonefish species ( Amphiprion percula) were protected from all the symbiotic anemone species tested, while most other anemonefish species were stung by at least one anemone species. The extreme host specialist, Premnas biaculeatus, was only protected from its natural host species ( Entacmaea quadricolor) and was stung by 6 other symbiotic anemone species. The juveniles of all anemonefish species were protected from E. quadricolor, but only a few fish species were able to contact Stichodactyla gigantea without being stung. Fish that were stung by anemone species with strongly adhesive tentacles (e.g., S. gigantea, S. haddoni), were generally captured and killed. However, there was no correlation between the tentacle adhesive force of an anemone species and the number of anemonefish species that it stung.

Do the Anemonefish Amphiprion ocellaris (Pisces: Pomacentridae) Imprint Themselves to Their Host Sea Anemone Heteractis magnifica (Anthozoa: Actinidae)?

AbstractJuvenile anemonefishes detect their host sea anemone by olfactory stimuli; in order to investigate whether this behaviour is innate or acquired, the anemonefish species Amphiprion ocellaris was bred in two different ways: 1. With no host sea anemone present at all (–A); and 2. With the specific host sea anemone Heteractis magnifica present in the hatching aquarium, so that these eggs were laid and hatched close to the sea anemone, as in nature (+A).The two different types of juvenile A. ocellaris were presented to the odours of the host sea anemone H. magnifica in two sets of short‐term experiments with the host (a) visually hidden in a net cage, and (b) visible but physically separated from the anemonefishes. In both cases, a water flow was established between fishes and host. The +A‐fishes found their host by olfactory and not by visual stimuli. In both series, the –A‐fishes showed a significantly lower affinity behaviour towards the odour compounds from the host sea anemone than the +A‐fishes did.A third type of experiment was a direct confrontation between fishes and host; here, the –A‐fishes were indifferent towards the host sea anemone for almost 48 h, while the +A‐fishes acclimated to the host sea anemone within the first 5 min of the direct confrontation.The results of this study suggest that Amphiprion ocellaris imprints itself olfactorily to its species‐specific host sea anemone Heteractis magnifica, and, furthermore, may be genetically disposed towards olfactory recognition of the host sea anemone.

Host selection, location, and association behaviors of anemonefishes in field settlement experiments

Nine anemonefish species were reared in the laboratory, and individuals were released in the field (Lizard Island, Australia and Madang, Papua New Guinea) at different distances and orientations away from natural (anemone species the fishes are found with in nature) and unnatural species of host anemones. Experiments were conducted to examine factors that could affect the settlement behaviors of the fishes: current velocity, distance and orientation of the fishes to the anemones, chemical vs visual cues, and presence of conspecific or heterospecific fishes. The fishes were usually attracted toward natural host species of anemones but not towards unnatural host anemone species nor to pieces of dead coral. Host selection during settlement provided the best explanation for the host specificity patterns displayed by anemonefishes in nature. The fishes used chemical cues released from the anemones to identify and locate the appropriate host species and could effectively locate the anemones from a maximum distance of 8 m downstream. Fishes released upstream or to the side of anemones (where anemone chemicals were assumed to be reduced or absent) were much less successful in locating anemones. The ability of the fishes to locate natural host anemones was strongly reduced when there was no water current. The presence of resident anemonefishes on host species of anemones did not influence the attraction behavior of anemonefishes released downstream from the anemones. Once the released fishes got close to or entered the anemones, the resident fishes would generally bite and chase them until the recruits left the anemones. Most fishes were not stung upon initial contact with the anemones.