The Hawaiian Dascyllus

by B. N. Sullivan

Cerianthid anemoneA few days ago I spent over an hour sifting through my photos, looking for images to use to illustrate a post about Cerianthid tube anemones. In addition to the ones I used for that article, I came across two photos that show a solitary, very tiny juvenile fish sheltering among the tentacles of a pretty Cerianthid tube anemone.

Here are the photos of the Cerianthid with the tiny fish. I made the images small so that both of them would fit into this post, but you can click on them to see a larger view. The little fish is a juvenile Hawaiian Dascyllus (Dascyllus albisella), a member of the Damselfish family (Pomacentridae). From its size -- not even a half-inch (15 mm) long -- we reckon the tiny fish was barely past its larval stage.

Hanging out with the Cerianthid is a good survival strategy for this little fish. Not only will it be somewhat protected, it also happens to eat the same kinds of things that are part of the Cerianthid's diet, like zooplankton. I've always wondered, though, how these tiny juveniles manage to locate such a host.

Cerianthid anemoneThis particular Cerianthid was located at a depth of about 36 meters, way out on a sandy plain with not much else of note in the immediate vicinity. There was no nearby reef -- not even a pile of rocks -- just a flat expanse of packed sand. Surely the little fishy didn't "see" the anemone out there on the sand in the middle of nowhere and decide to move in! I suppose there's some biochemical sensing at work.

The third photo on this page shows an adult Hawaiian Dascyllus, for comparison. As these fish mature, they lose those bright bluish-white spots on their foreheads completely, the white spots on their sides become very faint, and the jet black color in their scales becomes gray. The adults live in coral reef areas of coastal Hawaii where they are a common sight.

Hawaiian Dascyllus (Dascyllus albisella)The Hawaiian Dascyllus is a local endemic: it only occurs naturally in Hawaiian waters. If you think you've seen it elsewhere, you may have seen one of its 'cousins' of the same genus that look very similar. D. trimaculatus, in particular, looks very much like the Hawaiian Dascyllus, and the juveniles of the two species are virtually identical in appearance. That species is widely distributed around the Indo-Pacific region. We've seen it in the Red Sea, and also in the waters around Indonesia and Malaysia.

I took the photos of the Cerianthid and the juvenile Hawaiian Dascyllus off the coast of Puako, Hawaii. I photographed the adult in Honaunau Bay, on the South Kona coast of Hawaii's Big Island.

5 comments:

  1. Beautiful! And it is an interesting question, how the young fish find Cerianthids.

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  2. How very anthropomorphic! The bright, cute little children growing into homely, grey adults. I can almost see the lunchpail and car keys under the big one's ventral fins.

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  3. @ Alex - Thanks. I'm pretty sure there's some biochemical sensing involved, but the specifics are a mystery.

    @ Lavender - LOL, you've planted a very funny image in my head!

    Bobbie

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  4. That is pretty interesting. What's the possibility that the eggs were laid there or transported by mom? I don't know. It just reminds me of the breeding nest in a home fish tank where the little babies can hide.

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  5. Hi 2Sweet - That is a very logical theory for an aquarium, and I can see why you would propose it, but in the ocean things happen a little differently. With some exceptions, when the eggs of most critters hatch, they float away from wherever they were deposited. They disperse in the water column and are carried here and there by tides and other currents. Many animals spend their entire larval stage suspended in the water that way. As a result, the post-larval animal can end up miles from where its parents live.

    (I probably should do a whole post on this subject...)

    Bobbie

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