Recently our Fish Team processed some bycatch specimens that had been sent to us by MPI Scientific Observers. In one box were not one, but four specimens of a rare species of a frogmouth fish. Not only that, the biggest one was a world record.
So what are Frogmouths? Not to be confused with the bird with the same name, these frogmouths (also called seatoads, and coffinfishes) are a comical-looking ‘frog-shaped’ group of marine fishes found in tropical to temperate waters on reefs down to about 500 m depth.
They are usually small, about fist size (150 mm long); the largest to date has been a whopping 275 mm (a fluffylure frogmouth caught off Japan). These fishes are related to the iconic deep-water anglerfishes, but they have opted for a more sedentary lifestyle, living on the seafloor.
Along with cousins the batfishes and goosefishes, they have short, stumpy, thickened pectoral and pelvic fins positioned low on the body. Frogmouths have loose baggy skin, small fins, and an overall blobby shape and an enormous wide mouth (hence, the common name).
As their shape and position of the fins suggest, these fishes ‘walk’ across the seafloor on these fins, and is probably their preferred way of getting around. Streamlined and sleek these fishes are not!
They also share characters with all others in the order Lophiiformes, a highly modified first dorsal fin ray, right over the mouth between the eyes and topped with a fluffy tuft.
In frogmouths the lure is small (not what most people think as a big ornate lure as in deep-water anglerfishes) and it is waved to attract attention from potential prey, but more on that later.
In New Zealand, we currently have six species of frogmouth, five recently described since 2010. The specimens recently collected by MPI Observers is one of these: yellowspot frogmouth, Chaunax flavomaculatus, described in 2013 by Taiwanese scientist Hsuan-Ching Ho. It is a rare species, only previously known from two small specimens (105 and 122 mm SL), off north-eastern New Zealand, and a possible third from New Caledonia.
Within the new collection of four specimens, we discovered to our surprise that the biggest specimen broke the size record for the species, by a long way, it also broke all size records for frogmouths worldwide.
This monster is an incredible 321 mm standard length and weighs 2.3 kg, which is 2.5 times larger than previously recorded for the species and 1.2 times larger than others in the family.
With this ‘large’ new collection of four specimens now registered in the National Fish Collection, we know a lot more about the species’ size and distribution, and with further research, we will better understand the variation in character traits such as fin ray numbers and sensory systems.
The four new specimens also revealed beautiful fresh colours: a complex pattern of yellow, to yellow-green spots and blotches, outlined in a darker red, over a pinkish background. The belly was a uniform pink. Their lures were topped with a greyish fuzzy mop, with a couple of specimens having yellow hues. Kermit never looked this good.
But wait, there’s more!
As it thawed, we became aware that there was more that the biggest fish was going to tell us. What we first thought was a frozen lump of baggy skin, quickly became apparent was the last meal eaten before capture.
After photographing to get the fresh colours (these can fade rapidly as it thaws), we carefully dissected the fish to open the stomach. The stomach is rubbery (to stretch and accommodate large items), and black (to mask any bioluminescence released by a meal).
What we found was a large, near-perfect specimen of the endemic Orange perch (Lepidoperca aurantia), 205 mm long (~64% the size of the frogmouth) and 325 g in weight. This was a species described by curator Clive Roberts back in 1989. That specimen was also registered and incorporated into the collection.
The MPI Observer also recorded very important habitat information and included what else came up with these specimens: sponges, corals and rocks.
The complex colour patterns over the fish camouflage them against the seabed among these other items. Unwary prey venturing too close, investigating the wavy lure, is engulfed by a lightning strike.
The baggy skin even has a purpose. A video of another species on the Kermadec Ridge showed that when the ROV approached it, the frogmouth inflated its skin and raised itself up on its pelvic fins to appear larger. Given the size of the ROV, that was one ballsy little fish, it wasn’t going to let anything push it off its patch!
These discoveries show us that, even in relatively well-fished shallow areas, the shelf waters around our coasts still have new and exciting things to show us.