During a shore dive near Victoria, BC I was very surprised to see this unusual glassy tunicate (Ascidia paratropa) with what looked like fish eggs inside! However, on the dive I really didn’t know what type of tunicate I was looking at, but the round spheres inside one of the siphons appeared to be eggs. This tunicate also looked interesting to me with very large lobes extending from its body.
Later that day when I tried to identify the tunicate at home, it didn’t seem to match any of the photos in my collection of invertebrate ID books. So, I contacted Neil McDaniel who is a marine life researcher and videographer. Neil showed great interest, and started a discussion with other experts including Andy Lamb, a Pacific Northwest marine life specialist. Danny Kent of the Vancouver Aquarium came into the conversation as well, and identified the spheres seen within the tunicate siphon as fish eggs.
Tap on the image below to see a close-up of the fish eggs within the tunicate siphon.
The idea of a fish laying eggs in a tunicate is very interesting as I would imagine the tunicate would try to close its siphon and prevent the eggs from being deposited in the first place. This type of activity of a fish laying its eggs within a tunicate has not been recorded before in British Columbia.
Danny Kent quickly organized a dive team to come to Victoria and check out this discovery. Their dives were successful and tunicates with eggs inside were found. Samples were taken back to his laboratory at the Vancouver Aquarium, where the eggs have now hatched and small fry are developing. The fry are still too small for positive identification of the fish that deposited the eggs, and a few more months of growth may be needed to determine the species involved.
The Vancouver Aquarium has since published an article on this discovery.
Andy Lamb has also added this photo to his online book “Marine Life of the Pacific Northwest,” and has determined the tunicate to be an unusual variation of the glassy tunicate. His original 2005 hard cover publication is an excellent resource for marine life ID in the area that I’ve enjoyed for many years.
Andy Lamb’s online book is very current and has been continually updated since the original 2005 printed publication. This online resource can be found through KnowBC.
It is actually very ingenious of a fish to lay its eggs within a tunicate. The tunicate offers protection from predators and also a constant oxygenated water flow over the eggs. I’m very curious to see the results of Danny’s research, and learn which ingenious little fish is hiding its eggs in the protective cavity of these tunicates.
Danny Kent and his team have found it’s the fringed sculpin (Icelinus fimbriatus) that has developed this fantastic technique of protecting their young within the glassy tunicate.