One of our members sent in some footage of a flounder catching and eating a toxic toad fish, adding” Recently I spotted a large flounder and followed it about over some time and was lucky enough to get some footage of it catching and eating a toad fish. It’s really quick though and I had to watch it a few times to be sure.
“Until seeing this, I had thought that toadfish were not predated by other fish due to their toxicity. The flounder had only one eye and especially had a thing for chasing toad fish, but this is the only one I saw it catch.
“It could change colour immediately swimming over different ground, and I found that even looking away momentarily (for camera settings) it was often difficult to easily locate it again due to its effective blending with the sand below.
“…. (it had) two dark blotches on it, but I noticed that, when it was on the white sands, the dark blotches would also disappear mostly, which for a while caused me some difficulty in identifying it.
“I only rarely see any flounder(s) and usually they are much smaller than this one, but I did see another large one caught on the Brighton Jetty recently.
This photo shows it scaled with a watch: –
A close-up of its head
“The footage, which can be found on YouTube at https://www.youtube.com/watch?v=8xXYm7YdP1Q, shows it changing colour from starting on sand and swimming across a weedy area.”
Our observer had also said, ”
I identified as a long-toothed flounder by the two dark blotches on it, but noticed that when on the white sands the dark blotches would also disappear mostly which for a while caused some difficulty in identifying it. Please let me know if this is/is not a correct identification.
I only rarely see any flounders and usually they are much smaller than this one, but did see another large one caught on the Brighton Jetty recently.”
We tried to help to identify the flounder, but long-toothed flounder was unknown to us. Perhaps it was a Largetooth Flounder Pseudorhombus arsius. This is the name used on iNaturalist and all of my ‘fish’ books use that name. Details can be found at Largetooth Flounder (Pseudorhombus arsius) · iNaturalist. According to that page:
Our observer said that the flounder sighted had “two dark blotches on it. According to Largetooth Flounder (Pseudorhombus arsius) · iNaturalist (Source Wikipedia) “Pseudorhombus arsius, the largetooth flounder, is a species of left-eyed flatfish. As an adult, the dark side of its body, where its eyes are located, is on the left side. It belongs to the family Paralichthyidae. ….. ” Then further down (not from Wikipedia),”The body is greenish to pale brownish in colour and is normally marked with variously sized rings, and there is frequently two dark blotches on the straight and the curved sections of the lateral line with a smaller blotch which is half-way to the caudal-fin peduncle. It can vary the colour of the body so that it closely matches the surface the fish rests on.”
I see that Rudie Kuiter’s “Guide to Sea Fishes of Australia” says Small-tooth flounder, Pseudorhombus jenynsii, are , “Variously spotted. Usually 4 larger spots, standing out from other pattern, centrally placed as in corners of square box, each whitish with black centres and surrounds, and fifth similar spot behind, midlaterally and halfway to caudal fin.”
It then says that Large-tooth flounder are “Very similar to Small-tooth flounder, but with smaller spotted pattern, larger mouth and centre of caudal fin more pointed. Small but distinct white spot at end of pectoral-fin base ….”
Here is that photo again, showing the colouring and pattern of the sighted flounder: –
It certainly has a pointed caudal fin, although the colouring and pattern resembles the Small-tooth flounder featured in Rudie Kuiter’s “Guide to Sea Fishes of Australia” (other than the caudal fin). The Large-tooth flounder in “Coastal Fishes of South-eastern Australia” by Rudie H. Kuiter has a caudal fin more pointed than that of the Small-tooth flounder, but one could be forgiven for leaning towards the Small-tooth flounder due to its colouring and pattern. It has the spots described as “dark spots or rings with centre spots”. The spots on the Large-tooth flounder are described as “small to moderate-sized spots, or small circles”.
I cannot make any tooth details in this photo of the flounder’s mouth at all: –
Those dorsal fin rays near the flounder’s mouth resemble those for the Small-tooth flounder in “The Marine and Freshwater Fishes of South Australia” by Scott, Glover & Southcott (1974). Perhaps the jaw as well. Occurrence of the species is said to be “not very common” and its diet is said to include “prawns and small crabs”. The spots are described as “darker spots and marks, of which five large ocelli are most prominent. The ocelli are usually provided with a number of small white dots, and are surrounded by a dark ring”.
I feel that this describes this sighted flounder. As for our ‘one-eyed’ flounder, “The Marine and Freshwater Fishes of South Australia” says that “A narrow ridge separates the eyes”, and “the fins are spotted” as in the photos above.
The Small-tooth flounder (& the Large-tooth) features in “Sea Fishes of Southern Australia” by Hutchins & Swainston (619, & 618). It causes me to still lean towards the Small-tooth flounder. The caudal fin of the Large-tooth flounder is more pointed than that of the Small-tooth, unlike in this photo: –
Society members had concerns about the flounder eating a toxic toadfish. This created some discussion, such as: –
“Not all Toadfish (whether Smooth or Weeping or any other species doesn’t matter AFAIK) are toxic all the time.
Their ability to concentrate Tetrodotoxin in their liver and skin or other body tissues depends on a number of factors:- season, location, dominant type of food consumed by the puffer, maturity of the puffer come to mind but there are others.
And I’m now going to speculate (guessing, basically) that this predatory flatfish [and probably other carnivorous bottom dwelling fish groups, e.g. flathead, stargazers, even Stingarees and Stingrays – especially bigger rays like Smooth rays – can sense when a locally common, thus potentially important prey species – in this case Smooth Toadfish (which are exceedingly common here especially in late summer and all autumn) – is highly toxic or minimally toxic.
Or it may be largely dependent on relative size. A big flounder may be able to easily handle the small amount of toxin in a small Smooth Toadfish, whereas a juvenile or small adult flounder may avoid eating all but the tiniest Smooth Toadfish (as you know, we see some really tiny Toadfish, less than 10mm long, including Smooth babies and Prickly babies, at this time of year), which can’t possibly have accumulated enough toxin in their short lives to threaten large predators, unless they are consumed in vast quantities. So all the adult flounder needs to do is vary its diet, eating a few toadies, but also some goatfish, hardyheads, gobies, blennies, juvenile Moonlighter, Magpie Perch, Leatherjackets, etc.. etc.., and it won’t suffer ill health from the Tetrodotoxin in the puffers.
Digressing a bit, no species of fish has a single defence mechanism.
For Toadfish of all types, Tetrodotoxin concentration from down the food pyramid is an important defence ploy, but not 100% reliable (Tetrodotoxin availability is so varied between locations and seasons).
So they also have their inflation ploy (hence “puffer “) and their burial ploy, plus cryptic skills to name a few. And the good old “suddenly swimming very fast and erratically to escape” ploy,which almost every fish nature’s invented will employ if necessary.
PPS: Why have I mentioned Smooth Stingrays,and other rays? (and I forgot to mention bottom dwelling sharks).
Answer: Toadfish are mostly diurnally active,and often spend the night buried in sand, silt or shellgrit. So rays must frequently trap them via their usual feeding method i.e. placing themselves like a blanket on the bottom and then eating whatever they want trapped beneath (crabs, molluscs, fish, worms). I think it’s safe to assume that a big stingray would happily eat any Toadfish it trapped that way, and the Toadfish would have to have a very high Tetrodotoxin content to be a deterrent in the evolutionary sense. That said, Stingrays locally probably take the middle approach by mainly eating crabs, shells, cephalopods and worms, with the occasional puffer thrown in. And they may deliberately ignore (allowing escape) puffers they have trapped when they have sufficient other dietary choices. So, as long as they are finding plenty of yummy crabs and molluscs, why bother eating even slightly risky foods such as puffers? Horses for courses.”
Meanwhile, I told our observer, “It would be unusual for any flounder species to have just one eye. The second eye should have migrated from the other side early on. Where did you get ID of Long-tooth from? The old fish handbook says that Large-tooth are uncommon and usually over 15m depth. Small-tooth are also uncommon in the gulf. Is Long tooth the same as Large tooth? Large and Small tooth are similar but snouts differ and dorsal fin on Small doesnt extend quite as far forward. There is slight difference in the colour patterning.”
According to “World Atlas of Marine Fishes” by Rudie H. Kuieter and Helmut Debelius, there were (in 2006) ca. 100 species of Family Pleuronectidae (right-eyed f lounders) of ca. 45 genera, ca. 30 species of Family Paralichthyidae (Large-tooth flounders) of ca. 5 genera, and ca. 90 species of Family Bothidae (Left-eyed flounders) of ca. 15 genera.
Only about 6 of these some 220 species seem to occur in SA waters, and only 4 of those 6 seem to occur in SA waters.