Clown Anemonefish Amphiprion Ocellaris Research Articles

Finding Nemo\u2019s clock reveals switch from nocturnal to diurnal activity

Timing mechanisms play a key role in the biology of coral reef fish. Typically, fish larvae leave their reef after hatching, stay for a period in the open ocean before returning to the reef for settlement. During this dispersal, larvae use a time-compensated sun compass for orientation. However, the timing of settlement and how coral reef fish keep track of time via endogenous timing mechanisms is poorly understood. Here, we have studied the behavioural and genetic basis of diel rhythms in the clown anemonefish Amphiprion ocellaris. We document a behavioural shift from nocturnal larvae to diurnal adults, while juveniles show an intermediate pattern of activity which potentially indicates flexibility in the timing of settlement on a host anemone. qRTPCR analysis of six core circadian clock genes (bmal1, clocka, cry1b, per1b, per2, per3) reveals rhythmic gene expression patterns that are comparable in larvae and juveniles, and so do not reflect the corresponding activity changes. By establishing an embryonic cell line, we demonstrate that clown anemonefish possess an endogenous clock with similar properties to that of the zebrafish circadian clock. Furthermore, our study provides a first basis to study the multi-layered interaction of clocks from fish, anemones and their zooxanthellae endosymbionts.

Behavioural differences between breeding and nonbreeding pairs of protandry monogamous false clown anemonefish Amphiprion ocellaris

Anemonefishes are some of the most popular marine ornamental fishes. Due to the adverse impacts of commercial fishing on the wild populations of anemonefishes, a more suitable and efficient captive breeding programme must be promoted. In the wild, anemonefishes are protandrous sex-changing fish, but when two immature individuals with ambisexual gonads are raised together in captivity, the two differentiate directly into a male and a female, to form a breeding pair. However, not all the formed pairs spawn, explaining the great care required in captive breeding. This behaviour appears to be counter-adaptative, as anemonefish social groups form randomly in the wild, and such phenomenon would disturb their breeding success. This study evaluated the behavioural and physiological differences between breeding and nonbreeding pairs of false clown anemonefish Amphiprion ocellaris under captive conditions. Behavioural observations revealed that nonbreeding females monopolized the shelter provided, whereas breeding females allowed breeding males to use the shelter and the pair frequently stayed together in the shelter. Both nonbreeding and breeding females possessed mature ovarian tissue and similar level of plasma estradiol concentrations, but nonbreeding males had a smaller amount of testicular tissue and lower plasma 11-ketotestosterone levels compared to breeding males.

Steroidal regulation of the aromatase gene and dominant behavior in the false clown anemonefish Amphiprion ocellaris

The interaction between cortisol and aromatase may be a critical factor in sex determination or sex changes in teleost species. High cortisol concentrations inhibit transcription of the aromatase gene, resulting in masculinization. Anemonefish (Amphiprion spp.) are socially controlled, protandrous sex-changing fish, with a monogamous mating system. Females are the largest and most dominant members of social groups, second-ranking individuals become males, and other individuals remain nonreproductive. Individuals that change from male to female display high plasma cortisol concentrations, contrary to a previously established mechanism of masculinization. We investigated the effects of exogenous steroids on gene expression in the brain and gonads and on the occurrence of dominant behavior in the sexually immature ambisexual false clown anemonefish Amphiprion ocellaris. Transcription of the cyp19a1a aromatase gene increased in the gonads of estradiol pellet-fed fish but decreased in cortisol pellet-fed fish. Dominant behavior intensity significantly increased in estradiol pellet-fed fish, but decreased in cortisol pellet-fed fish. Methyltestosterone had no apparent effect on gene transcription or behavior. These results suggest that the masculinization mechanism induced by cortisol is common among teleost species, including protandrous sex-changing fish, and that behavioral changes induced by steroid supplements reflect social status in A. ocellaris.

Reduced Genetic Diversity in the Clown Anemonefish Amphiprion ocellaris in Exploited Reefs of Spermonde Archipelago, Indonesia

Populations of the clown anemonefish in Spermonde Archipelago, one of the main collection sites for ornamental fish in Indonesia, are potentially overfished, which might lead to a reduction in population size and genetic diversity. Loss of genetic diversity can reduce the adaptability, population persistence and productivity of the targeted species. Therefore, a study investigating the genetic diversity and its potential correlation to population densities of A. ocellaris was conducted. Two islands were chosen as study sites that differed in the degree of exploitation. Barrang Lompo has a high fishing pressure, whereas Samalona has less. Underwater visual censuses showed that population densities in Samalona were threefold higher than in Barrang Lompo (p = 0.005). Analysis of eight microsatellite loci in 364 tissue samples of A. ocellaris revealed that genetic diversity (numbers of alleles, private alleles, and allelic richness) was significantly reduced at the island with high fishing pressure. Allelic richness was also positively correlated with fish density (p < 0.05). These results indicate that ornamental fishery might be a factor contributing to the loss of genetic diversity in A. ocellaris. Therefore, the marine ornamental trade in Spermonde Archipelago needs to be managed (e.g. management of the fishing strategy, implementation of marine protected areas, regular monitoring and quota determination). Otherwise the populations of A. ocellaris might collapse.

Use of Clove, Mint and Camphor Essential Oils on Confinement of Clown Anemonefish Amphiprion ocellaris (Cuvier 1830): Anesthetic Effects and Influence on Water Quality

The aim of this study was to evaluate the anesthetic efficacy of essential oils of clove, mint and camphor to clownfish Amphiprion ocellaris and their effects on water quality in simulated confinement transport conditions. Anesthetic effects of clove, mint and camphor oils were tested at concentrations of 2.5, 5.0 and 7.5 μL L-1; 20, 25 and 30 μL L-1; and 100, 120 and 140 μL L-1, respectively. Confinement periods of 6 h, 12 h and 24 h were simulated (n=8 fish/time/concentration). Animals were randomly selected and transferred to polyethylene bags (16 × 30 cm, 5 fish L-1). Water concentrations of dissolved oxygen (DO), nitrogen in the form of total ammonium (N-TA=NH3+NH4 +) and non-ionized ammonia (N-NH3) and pH were measured before closing and after opening the bags. Different confinement densities of A. ocellaris (5, 10, 15 and 20 fish L-1) were tested in polyethylene bags containing water and anesthetics essential oils. Concentrations of 5, 25 and 120 μL L-1 (clove, mint and, camphor oils, respectively) were used during 24 h of confinement. Water-quality parameters monitored were the same as in the previous experiment, with addition of measuring concentrations of dissolved CO2 in water. The use of mint oil (25 μL L-1, maximum density of 10 fish L-1) significantly reduced the concentration of N-TA. At low densities (5 fish L-1) clove (5 μL L-1) and camphor (120 μL L-1) oils can also be safely used for confinement of Amphiprion ocellaris for 24 h.

Socio-economy of marine ornamental fishery and its impact on the population structure of the clown anemonefish Amphiprion ocellaris and its host anemones in Spermonde Archipelago, Indonesia

The clown anemonefish ‘Nemo’ Amphiprion ocellaris is the most popular fish species in the global marine ornamental trade and also its host sea anemones Heteractis magnifica, Stichodactyla gigantea, and Stichodactyla mertensii are traded. However, total catch and the potential impact of exploitation of these target organisms in Spermonde Archipelago, Indonesia, are not known. Therefore, the main objective of this study was to investigate the impact of the fishery on populations of A. ocellaris and its host anemones and how management could be improved. In order to obtain a comprehensive view on the marine ornamental fishery and trade of these species in Spermonde, this study also investigated the socioeconomics of the marine ornamental fishery and the catch records for A. ocellaris and it's host anemones. The study revealed that both, A. ocellaris and sea anemone densities were significantly lower at coral reefs with high exploitation (HE) than at reefs with low exploitation (LE). The total body length and group size of A. ocellaris was also significantly smaller at HE than at HL sites. The yearly amount traded by middlemen is estimated to 140 000 specimens of A. ocellaris and 31 000 anemones. The socioeconomic analysis showed that educational level of marine fishermen family members was low; most of them only finished elementary school. The household income analysis showed that marine ornamental fishery was not the major source of income, covering 13−43% of the expenses, with the exception of one studied island (84%). These findings revealed a considerable negative impact of marine ornamental fishery on the target populations and therefore, the implications for management strategies and conservation are discussed, including fish size restrictions for collectors, marine protected areas and regular monitoring of the amount of trade at middlemen.

Consistent behavioural traits and behavioural syndromes in pairs of the false clown anemonefish Amphiprion ocellaris

Using the social clown anemonefish Amphiprion ocellaris, whether individuals exhibited consistency in activity levels, boldness and sociability in a paired context, and whether these three behavioural traits were positively correlated within a single behavioural syndrome, was investigated. The results highlight that consistent individual differences in behaviour are expressed in a social fish and suggest that consistent behavioural traits and behavioural syndromes could influence the structure and functioning of their societies.

No evidence of shelter providing a metabolic advantage to the false clown anemonefish Amphiprion ocellaris

There was no evidence that shelter conveyed a metabolic advantage to the false clown anemonefish Amphiprion ocellaris in terms of standard and routine rates of oxygen uptake. The metabolic and fitness benefit of shelter might not, therefore, be widespread among all fish species.

Immunohistochemistry of Brain Arginine Vasotocin and Isotocin in False Clown Anemonefish Amphiprion ocellaris~!2009-12-08~!2010-04-14~!2010-06-29~!

The brain nanopeptides arginine vasotocin and isotocin are considered to be involved in the regulation of social and reproductive behavior in teleosts. We investigated the immunoreactivity of brain arginine vasotocin and isotocin neu- rons in four pairs of the protandrous false clown anemonefish Amphiprion ocellaris (Cuvier, 1830). After 450 days of pairing, the social rank of each individual was clearly distinguishable by body mass. The resident-intruder model test re- vealed that dominant individuals tended to display agonistic behavior more frequently than subordinate individuals, yet pairing failed to induce sex differentiation by social rank (i.e., gonadosomatic index and steroid profiles did not differ sig- nificantly and the gonads were ovotestes in both social rank individuals). However, dominant individuals had a larger size of arginine vasotocin neurons in the magnocellular layer and a greater number of isotocin neurons in the parvocellular layer of the brain preoptic area (POA) than did subordinate individuals. Arginine vasotocin and isotocin neurons of each layer of the POA showed different projection patterns: in the magnocellular layer, the fibers innervated the medial zone of the telencephalon and the mesencephalic tegmentum, but not in other layers. These results suggest that vasotocin and iso- tocin neurons in the brain of A. ocellaris regulate social behavior and have different roles.

Incorporating fine‐scale seascape composition in an assessment of habitat quality for the giant sea anemone Stichodactyla gigantea in a coral reef shore zone

AbstractHabitat loss due to land reclamation often occurs in sandy coral reef shore zones. The giant sea anemone Stichodactyla gigantea, which harbors the false clown anemonefish Amphiprion ocellaris, both of which are potentially flagship species, inhabit these places. To assess habitat quality for S. gigantea, we examined correlative associations between the number and the body size of S. gigantea and the amount of habitat types in fine‐scale seascape composition quantified from an enlarged section of a high‐resolution (1/2,500) color aerial photograph of the shallow shore zone of Shiraho Reef, Ishigaki Island, Japan. This study confirmed that anemones were most abundant at the edges of dense seagrass beds characterized by shallow sandy bottoms, rock beds, and sparse seagrass beds, while they were less abundant in coral patch reefs. However, anemones inhabiting coral patch reefs were significantly larger and their rate of disappearance over 3 years was lower than those inhabiting other habitats. This suggests that coral patch reefs may be more suitable habitats supporting larger animals and greater persistence of S. gigantea. The visual census techniques applied here, combined with aerial photography and image‐analysis software, may be useful as a simple analytical tool for local assessment of suitable habitats for relatively small‐bodied marine fauna in shallow‐water seascapes.

Effects of copper on survival and growth of larval false clown anemonefish Amphiprion ocellaris

Larval false clown anemonefish of about 12h after hatching were fed newly-hatched brine shrimp nauplii in natural (control) and copper-added seawater (40–640 μg-Cu/L) at 26.5±0.5°C for 14 days. Survival rate of the fish increased with increasing copper concentrations up to 160 μg-Cu/L. The rates at 80 and 160 μg-Cu/L were 65 and 80%, respectively, and were significantly higher than that of the control (30%). A positive effect of copper addition on the survival rate was also observed in the other rearing experiment with the fish from seven different spawning chances. Growth rate of the survival fish was not affected by copper concentrations. The copper concentration of the survived fish increased with increasing copper concentrations in the rearing water.