Underwater Fish Wash!
Location: Alice's Backside - Ginger Island, BVI
by Wayne & Karen Brown
We are back at Alice's Backside, again. This was our dive site on Day 4 and Day 7. Cori was taking us to visit a different location, but when we got there it was too choppy and the current was too strong. Just like on land, underwater things can be affected by weather, too! Because of the direction the winds are blowing today Alice's Backside is on the side protected from the wind by Ginger Island.
Since we have investigated the corals at Alice's Backside on our other dives today we will have a chance to spend more time looking at the fish.
After we put on all of our scuba equipment we jumped into the water. We are surprised to see that we are surrounded by a school of barracuda! Actually these are not barracuda, but long, silvery fish that look like small barracuda, called southern sennets. These fish are about 14 inches long and are in the same family as barracudas. Southern sennets don't grow as long as barracudas (18 inches compared to 6 feet long). Southern sennets also do not have the same bad, but undeserved, reputation that barracudas do.
There are about 100 southern sennets in this school. These fish are not interested in us because they eat only small fish. They are swimming all around us but they don't come any closer than about 4 feet away from us. When we slowly swim toward them they move away from us keeping their 4 foot distance.
We squeeze the on button on our DVs and the sennets move aside opening up a hole in the school like a big donut hole! We zoom through the school of fish like a jet plane zooming through a cloud.
We cruise over the reef about 50 feet underwater. Next to one of the coral heads we see a fish is stopped and not moving. We stop and set our DVs on the sandy bottom so we can take a closer look without scaring the fish. We are watching a bluestriped grunt (about 10 inches long) getting cleaned!
Fish don't have hands and arms like you do so they can't brush their teeth or scratch their backs. When fish get dirty small cleaner fish clean them off. It's like an underwater car wash for fish! The cleaner fish we see are two sharknose gobies about 1 1/4 inches long. The grunt could easily eat these tiny gobies, especially when they swim inside the grunt's mouth to clean its gills and teeth. The cleaner fish are not afraid of the bigger fish because they know they are safe. The bigger fish never eat the cleaner fish because they know cleaner fish help them stay clean.
While small fish are usually hiding from bigger fish, cleaner fish sit right out on top of the corals where the bigger fish can easily see them. When a big fish wants to be cleaned it will stop next to the coral and let the cleaner fish hop on its back and start their cleaning. The cleaning may take a minute or so. When the bigger fish feels like it is all clean it will wiggle. That is the signal to the cleaner fish that their job is done. They hop back on the coral, the bigger fish swims away and they wait for their next customer. Just like cars lined up at the car wash to be cleaned we see fish lined up at the "fish wash" waiting their turn to be cleaned! The cleaner fish don't get paid, but they do get a free meal by eating the bigger fishes' parasites or food stuck between their teeth.
Fish cleaning is part of something called symbiosis. Symbiosis is a big word made out of two smaller words: "sym" and "bio". "Sym" means "together" and "bio" means "life". Symbiosis means how things live together. Some animals live as friends with other animals. (The cleaner fish are friends with other animals.) Some animals live as enemies of other animals.
The little sharknose gobies are not the only cleaners of the sea. Other gobies and small fish are cleaners, too. There are even shrimp that work as cleaners. We see one of these cleaner shrimp on the sandy bottom in a small sea anemone. It is a shrimp called a Pederson cleaner shrimp. It is only 3/4 inch long! This tiny shrimp is sitting on the tentacles of the sea anemone and waving its long antennae to attract fish customers. We don't see any fish customers waiting to be cleaned, so Karen decides to get cleaned! With her fingers together she slowly sticks out her hand next to the sea anemone. After a few seconds the cleaner shrimp hops on her fingers to clean them off! The cleaner shrimp scampers around her fingernails pulling off tiny bits of dead skin to eat. ("It doesn't hurt. I kind of tickles!") After about 30 seconds of cleaning the shrimp hops off Karen's fingers, back onto its anemone and starts waving its antennae to attract another customer!
Symbiosis is not always good for other animals. Under a coral head nearby we find symbiosis that is bad for other animals. We see a pretty fish, called a red hind, about 10 inches long. A red hind is a type of grouper. Because of their reddish spots they are also called strawberry groupers.
This red hind looks perfectly normal and healthy until we see the right side of its head. On its cheek, just below its eye is what looks like a tiny (about 3/4 inch) lobster without claws! This is not a tiny lobster. This is a parasite called an isopod. This is like an underwater tick! At night while the fish is sleeping a isopod will jump on the fish's head and dig its claws into the fish's skin so the fish can't knock it off. Then the isopod drills it sharp mouth into the fish's skin and it sucks THE FISH'S BLOOD! This is good for the isopod, but bad for the fish. This type of symbiosis is not good for the other animals.
There is no way we can take the isopod off the fish. The fish would be scared of us if we came too close and would swim away. The fish would not know that we are trying to help it. Fortunately the isopod will not kill the fish. The isopod only takes a small amount of blood and the fish will not be seriously hurt. The fish will probably live out its normal life span.
Well, our dive computer shows us that our air is getting low. We should be heading back to the boat and get out of the water. As we zoom on our DVs back to the boat we are glad that we are not a fish with an isopod sucking our blood! We are also glad that isopods only attack fish and not people!
Join us tomorrow as we take a snorkeling tour of some of the smaller islands of the British Virgin Islands and investigate whatever corals and fish we find.
Wayne & Karen
Alice's Backside, Ginger Island
Position: 18º 23' N / 64º 29' W
Air Temp: 82ºF
Weather: windy, overcast with high clouds.
Sea Conditions: rough seas, slight current
Dive Time: 1 hour 4 minutes
Maximum Depth: 54 feet.
Water Temp: 81ºF
Underwater Visibility: 60 feet
We have accidentally jumped into a school of southern sennets that surrounds us. These fish are about 14 inches long and in the barracuda family.
We found this bluestriped grunt (10 inches long) being cleaned! (Enlarge the picture to easily see the cleaner fish just to left and down from the center of the fish.)
These cleaner fish are sharknose gobies about 1 1/4 inch long. They are sitting on top of a brain coral waiting for another fish customer to clean.
Karen is getting her fingers cleaned by a tiny (3/4 inch) cleaner shrimp.
We found this red hind (10 inches long) with this blood-sucking parasite stuck on the side of its head!