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Dive Dry with Dr. Bill

#716: Finding Dory

Kids everywhere are probably familiar with the fish I'm writing about this week. Most of them have seen "Finding Nemo" and are familiar with Dory. I didn't see this movie until a few years after it came out when I was serving as marine biologist and underwater videographer on one of Lindblad Expeditions eco-cruise ships in Belize and Honduras.

Of course as a scientist, I knew that Dory might have been that one fish's preferred name but that the species was actually known as the palette surgeonfish (Paracanthurus hepatus). Of course that would be a mouthful for a little munchkin! They are also known as the blue tang, royal blue tang, regal tang, hippo tang, wedgetail blue tang, flagtail surgeonfish, blue surgeonfish and even chirurgien bleu (if you live in France). I think I see why she chose the name Dory! I didn't get a chance to film one until I dove the waters in the Philippines a few years ago.

Dory and her relatives are not found in the Caribbean except on film or in aquaria. They are native throughout the Indo-Pacific region including the Great Barrier Reef, Indonesia, the Philippines, Japan and East Africa. They prefer clear water over the exposed outer reef or areas with moderate to strong current.

The disc-shaped body is royal blue with a yellow tail. The pectoral fins are also yellow. The black design on the sides is the source of the name palette since it looks like an artist's palette. Structures known as iridophores are responsible for the blue color. These fish have small scales and a pointed snout. Body coloration may darken and/or the black markings may fade during mating, when males compete for dominance or when under stress. The kids are quite different with bright yellow bodies and fins with light blue edges.

Like other surgeonfish they possess scalpels, sharp spines located near the base of the tail, for defense. These spines contain a toxin that can be very effective against small predators. Humans should also exercise caution when handling these fish.

The youngsters prefer a diet of plankton, but adults add vegetables to theirs. They graze on the algae growing on coral reefs. In doing so they help maintain the health of the coral. This is typical of many surgeonfish. In areas where they have been overfished, coral is often overgrown with algae.

Fortunately for these fish, their flesh is reported to have a strong odor and is therefore not fished for food. In fact, like a number of other species, they may cause ciguatera poisoning in humans. They are a very popular fish in the aquarium trade, but are not easy to maintain. They require proper food and are often subject to disease and bacterial infection.

Like humans, males court the females vigorously and spawn in aggregations (breeding groups). They are believed to mate year-round. The species is a broadcast spawner with males and females casting their eggs into the water for external fertilization. They swim rapidly toward the surface when spawning, which helps ensure the eggs are dispersed by the currents rather than settling down on the reef. In some cases mating pairs may form with the male and female swimming around one another in circles. Been there, done that!

A drop of oil in the egg makes it float and the eggs hatch into tiny larvae in about 24 hours, drifting within the plankton so the youngsters can see the world before settling down. With such a short development time in the egg, the larvae that hatch are not fully developed. Initially the heart is not even beating and they remain in a resting state for a few hours. Over a period of about a week they begin swimming and the jaws and digestive tract form.

A potentially serious issue for Dory and her kin is the loss of coral habitat due to oceanic warming and coral bleaching. Of course dead coral can also become inundated with algal growth so further research into the effects of global warming on this species and its relatives is needed.

© 2016 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Dory and Nemo as movie stars and Dory in real life.

This document maintained by Dr. Bill Bushing.
Material and images © 2017 Star Thrower Educational Multimedia