I have written a few articles for UltraMarine Magazine over the past year or so and am pleased to have my first cover image with them this issue (Issue 33: April/May 2012). The cover shot is a pink anemonefish that I took at Wakatobi Dive Resort in Indonesia a few years ago. I’ve always had a soft spot for the image which I took with a very short depth of field, giving it an ethereal feel with soft pastel colours of the pale blue sky, purple mantle of the anemone and pinks of the fish.
My feature article in the same issue (see below) is entitled ‘Clowns in the Wild’ and is about the biology and conservation of wild anemonefish. Anemonefish are one of the relatively few captive bred marine ornamental fishes but there remain huge pressures on wild populations. For the marine aquarium trade to be sustainable I believe it is important that people make considered and educated choices on which species to keep. Where there is an option for a captive bred species this is by far the best choice. Apart from reducing demand on wild populations the fish are healthier, living longer and unlikely to infect the system with pathogens.
CLOWNS IN THE WILD – By Richard Smith (© Richard Smith 2012)
Anemonefish are one of the most charismatic fish both on coral reefs and in the home aquarium. They have become well known for their gregarious nature and symbiosis with anemones, less well known and unsurprisingly omitted from the popular ‘Finding Nemo’ movie is their propensity to change sex. Sadly, their sky rocketing popularity and environmental degradation are putting extreme pressure on wild populations.
Twenty-eight species of anemonefish are known: 27 belonging to the genus Amphiprion and a single species, the spine-cheek, to Premnas. They are believed to have originated in the ‘Coral Triangle’ region comprised of Malaysia, Indonesia, Philippines and Papua New Guinea that has acted as a crucible of diversity for many coral reef fishes. From this area, anemonefish spread across the tropical Indo-Pacific, and many indigenous species evolved at the limits of their geographic range. These include endemic species found only in the Red Sea, Lord Howe Island off eastern Australia and one limited to the waters off Madagascar. Interestingly, there are no anemonefish in the Caribbean as a result of the land bridge between North and South America acting as a barrier to their arrival.
As their name suggests, anemonefish have an absolute requirement for a healthy anemone and most will spend their entire post-larval life living in association with a single one. This symbiotic relationship benefits both the fish, through the protection it gains from the anemone’s stinging tentacles, and the anemone, due to the fish defending the anemone from its own predators. Protected by a mucus layer, the fish is free to dart in and out of the stinging tentacles where predators dare not follow. With this immunity from predation, the character of these fish has developed to be one of the most playful and cheeky of all coral reef fishes. They are so sure of themselves that they will sometimes leave their anemone to see off a perceived threat much larger than themselves. An overzealous fish once followed me for thirty or so metres until it realised it could no longer see its anemone home. The bravado was suddenly gone and it cowered on the sandy bottom. I began to swim back towards its home and luckily the fish followed and seemed very pleased to be reunited with its family!
The relationship between anemonefish and host becomes slightly more elaborate through the inclusion of a third, but equally vital associate. Within the anemone’s tissues live microscopic algae known as zooxanthellae. These are basically the same algae that live within the cells of many corals, and in much the same way they use the sun’s light through photosynthesis to produce nutrients that are used in the anemone’s metabolic processes. These algae, however, are extremely sensitive to environmental conditions and when stressed have a tendency to jump ship in a process known as bleaching. This is when algae leave the anemone’s cells to avoid the increasingly hostile chemical environment that develops within the warming tissues. The term bleaching derives from the ghostly white appearance of the anemone, or coral, that remains following the loss of these algae. Bleaching doesn’t automatically result in death but anemones tend to wither and succumb to disease without the help of these algae, with severe implications for their resident anemonefish.
The life-cycle of anemonefish is one of the most intriguing features of their biology. They are protandrous, which derives from the Greek meaning male first, and start life as a male and subsequently become female. Immediately after hatching and following a two-week planktonic stage, spent drifting in ocean currents, the young males find the reef using chemical cues in the water. They usually join an established group where a reproductive pair share their home with one or two non-breeding sub-adults. The largest fish in the group is always female and the next largest her mate. All smaller fish are suppressed from becoming sexually mature by the female’s social dominance. It is a waiting game for the anemonefish after arriving at their new anemone home. They are believed to live for up to thirty years, twice as long as other coral reef damselfish, and during this time they move up the ranks as their ‘superiors’ die off. Finally, following the death of the female, her dominance over the group is released and a strange process begins. Sperm producing cells in her mate wither and egg production begins. The male slowly begins to grow and eventually becomes a mature female, a process which can take as long as a year and a half. At the same time the next largest fish in line matures and assumes the role of reproductive male.
Elaborate reproductive system, symbiosis with anemones and the longevity of anemonefish all play a large part in their susceptibility to overfishing and habitat loss. Over the past couple of years I have seen, for the first time, large numbers of bleached anemones in southeast Asia. Recent studies have found that bleached anemones are less suited to accommodate anemonefish as they shrink and cannot sustain the same number of fish. Additionally, anemone death can occur under extreme and prolonged spells of poor environmental conditions. Like hard corals they are very slow growing and re-establishing themselves in areas decimated by bleaching can take many years. Anemonefish are extreme habitat specialists and their absolute requirement for a healthy anemone means that where there are no anemones there are obviously no anemonefish, a worrying trend as bleaching and damage to coral reefs becomes more commonplace.
The over-collection of anemones and anemonefish are also taking their toll on the populations of both in the wild. Whilst anemonefish are one of the most commonly bred marine ornamentals, the high demand surpasses supply. In 2002, anemonefish comprised 60% of the total aquarium trade catch in the Philippines. In Australia, anemone collection is prohibited and at least one fish, preferably the female, must be left to provide juveniles an odour by which they can find a suitable home. Since the female is the oldest and largest this is also likely to reduce the time before reproduction can recommence. Even so, anemonefish naturally spawn relatively infrequently, for a coral reef fish, producing eggs only twice per year and even in Australia populations have reduced since 2000. Another downfall for these species, particularly in unregulated areas, is the ease of harvesting them. Anemonefish seek refuge in their anemone rather than fleeing into holes so are easy targets for fisherman. Sadly however it is estimated that up to 80% may die between capture and reaching the home aquarium.
Luckily anemonefish are one of the relatively few captive bred coral reef fishes that are readily available. Advances in their husbandry have identified temperature and day length to play an important role in their spawning frequency and now at least seven species are regularly reared. They can be encouraged to spawn in relatively small tanks and attach eggs to terracotta pots or tiles adjacent to their anemone. The planktonic fry can then be reared in even smaller aquaria, which are used to mimic the open ocean stage of their life-cycle. Since marine ornamental aquaculture is in its infancy it is hoped that more species can be encouraged to reproduce in captivity. This is vital if the number of wild caught marine fish can be reduced from the current 90-99% to a more sustainable figure. Captive reared fish are hardier, fare better in captivity, survive longer as they’re generally younger on arrival at the home aquarium, harbour fewer diseases and are less likely to die from shipment stress.