I have reported via iNaturalist my sighting of a Striped Sea Louse, Creniola laticauda, on an Ornate cowfish, Aracana ornata, at Edithburgh jetty on 21st September 2025.
As I posted on iNaturalist, “This older juvenile/young female (Ornate Cowfish) has probably hosted a Striped Sea Louse, Creniola laticauda, judging by the extensive area of damage on its (Left) flank. I got a glimpse of the (Right) side during this brief encounter and couldn’t see any Louse or other external parasites, so I guess the Louse (presumed, based on typical damage for Creniola laticauda females) had already “jumped ship” (moved to a larger or softer host).”
“And thinking about my opening Notes, I’ll speculate further by asking these questions:
How often do we see Cowfish with Striped Sea Louses on them?
Quite often.
How often do we see Cowfish with such extensive tissue loss resulting from parasitism by Striped Sea Louses (Lice), (again, I’m presuming with regard to parasite species)?
Very rarely (indeed this is my first time, in 50+ years of SA diving).
Why so rarely?
Perhaps the Harmful Algal Bloom (HAB) is implicated. We know that Striped Sea Louse females were commonly observed on a wide variety of fish hosts at many popular dive sites in SA pre-HAB. The Louses (Lice) had plenty of choices, and it was unusual to find a host with extensive* surface tissue loss.
* (Proportional to host size. Which is not to say that the injury wasn’t serious; e.g. often an eye was blinded, greatly increasing the host’s predation risk and reducing their feeding ability).
But this very severe and prolonged HAB must have drastically reduced the number and variety of potential hosts. So, if we **assume that the Striped Sea Louses (Lice) themselves were not decimated by the toxic algal bloom, they would have had to spend more time on their current live host, thus consuming greater areas of external tissue. But not enough to kill the host, or the Louse would be forced to find another host, and that would not be easy with so few demersal inshore fish left alive and available.
** (Important caveat: that’s a major assumption, for which I’ve no evidence!)
(I had previously posted details of a Striped Sea Louse on a male Ornate cowfish on iNaturalist)
