March 3 - Neobenedenia melleni

Here’s Neobenedenia melleni, a pesky monogenean parasite on the skin and gills of tropical and subtropical fishes. It probably hails from the Caribbean, but will infect pretty much any warmwater marine fish with scales (for some reason it can’t or doesn’t infect eels and other scale-free fishes). N. melleni is a capsalid, a group that includes several species that are problematic in aquaculture. They can be damaging because they have a direct life cycle (no intermediate host) so in dense host populations like aquariums and aquaculture pens, they multiply rapidly. They mostly eat skin and mucus, which is a pretty renewable food source until it is removed faster than it can be replaced. At that point the fish suffers from salt and water imbalances and can die quickly or succumb to secondary infections. This photo shows a juvenile, with the head and “Mickey Mouse” anterior attachment pads at the top, the four pigmented eyes, the two excretory vessels and gut in the middle, and the large and complex posterior attachment organ or haptor, which features tiny marginal hooks, two pairs of major hooks in the middle, and a valve or seal flap around the edge. These guys invest a lot in staying attached, but when you are trying to hold onto wet fish skin in a viscous medium like water, you need to!

Contributed by Al Dove.