|Adult female with larval brood (left) and newly-hatched zuphea (right)|
Photos from Fig. 1 of the paper
There are over 190 known species of gnathiids from all across the world, but the full life-cycle has only been described for four of those species, and now G. maxillaris join that very short list. Even though G. maxillaris is relatively well-studied and fairly widespread across the Atlantic Ocean as well as the Baltic and Mediterranean seas, the complete life-cycle of G. maxillaris was unknown until now because much of this parasite's development takes place out of sight on the open sea.
But the infestation at Aquarium of Barcelona provided scientists with a great opportunity to study this life-cycle. They harvested G. maxillaris larvae by exploiting their natural attraction to light; at night, they turned on a set of light installed at the bottom of the aquarium, then pump the sea water through a fine-meshed plankton net that have also been placed there to trap the parasite larvae.
|Clockwise from upper left: |
Adult female, adult male, female carrying eggs
From Fig. 2 of the paper
They also discovered that G. maxillaris has different preference for specific parts of the fish's body, and this has consequences for the parasite's growth. While they can attach pretty much anywhere on the fish's body, they have a taste for the base of the fins, near the gill covers, or around the eyes - basically areas of high blood flow and where it would be harder for the fish to rub them off. They also noticed zuphea that attach themselves to the fish's fin feed for longer and takes more time to develop into a pranzia, most likely because there is less blood flow there than other parts of the body, so the parasite needs to stick around for longer to get a full meal.
In all, G. maxillaris' entire life-cycle takes about three months to complete, but that is if the water temperature is at 17.5 °C; if the surround temperature is 20 °C, then the parasite would take only two months to complete this cycle. At higher temperature, the female parasites also grew larger and produced more eggs. This is particularly pertinent to the current situation because one of the (many) consequences of increasing ocean temperature might mean in the future, the seas will be filled with more gnathiids that grow faster than ever before, which is bad news for fish. Not only are they blood-suckers, like ticks on land, gnathiids can also act as vectors for various other parasites.
While an infestation of tiny "ticks of the sea" might not be the best news for a national aquarium, when life hands you an infestation - you might as well do some science with it!
Hispano, C., Bulto, P., & Blanch, A. R. (2014). Life cycle of the fish parasite Gnathia maxillaris (Crustacea: Isopoda: Gnathiidae). Folia Parasitologica 61: 277-284.