22 February 2013

Meet the fascinating spotted ratfish

During one of my dives at Rock Bay, Vancouver Island, at a depth of 12 m two strange looking fish swam towards me. I knew the species only from drawings and a few photo's: dragonfish! I was astonished, because I thought this was a deep sea species that hunts in the dark. But now here, in this shallow water and at broad daylight?

It were two spotted ratfish, Hydrolagus colliei (NL: gestippelde draakvis). I don't think ratfish is an appropriate name. I prefer the Dutch (NL) name: draakvis, i.e. dragonfish. Because it looks like something mythical; an animal of long forgotten times. It belongs to the family of the Chimaeridae. Now we're talking, because that name refers to a mythical beast, the Chimaera.

The first time they swam towards me, they were not really interested, kept a distance of about 4 m and swam away. I know it is no use swimming after fish. They get frightened and just get away. After 20 minutes I saw them again at greater distance. I thought: let's be patient, maybe they are curious and will swim to me. In the back of my head I also thought of danger. A poisonous spine? How I knew I don't know. Maybe I read it years ago, maybe it was intuitive.

Bingo: after a while one of the two glided towards me. Observing me with its strange eye and keeping low, a few decimeters from the bottom, it came closer and closer. I was enthralled!

At that dive I used a 24 mm wide-angle lens and dome port. For close by shots of the head she (as it later appeared to be) had to swim within 'hands reaching'. So I was thinking: closer, come closer. She did! She came as close as 30 cm and must have seen herself reflected in the dome port. She swam away, turned and made it possible for me to make photo's of her profile from head to tail. As Canadians often say: awesome.

And the spine? Have a look at the first photo of this post and you see its first dorsal fin (= fin on its back) with the big spine going skywards at the last moment. That does not mean she was going to use it offensive. I think it is more like making an impression, showing off as a lot of fish do: here I am and don't mess with me, otherwise....

Afterwards I read in '151 Dives', an excellent book/diving guide by Betty Pratt-Johnson (2007): 'Avoid the spine. Once a ratfish bit my leg on a night dive. The only attack I have heard of yet, but beware.' Moen & Svensen (2004) about its Atlantic counterpart Chimaera monstrosa, also the ratfish or rabbitfish (NL: draakvis): '..has a stout spine connected to a poison gland that produces a deadly poison.' Deadly for humans?

© Wheeler: Fishes of the World

What's in a name? There are a lot of common names for members of the Chimaeridae: ratfish, rabbitfish, ghost shark, elephant fish. Hydrolagus means water hare. Compare that with rabbitfish. But what about rat, rabbit, hare or elephant: they don't like like it. Wheeler (1975) shines a light: 'Its name rabbitfish refers to its rabbit-like incisor teeth, while ratfish is in reference to its very long tail.' I keep on nagging about names: the tail of the spotted ratfish does not look like a rat's tail at all, contrary to its Atlantic nephew. Compare the drawing overhead of Chimaera monstrosa (Wheeler, 1975) with my photo's of Hydrolagus colliei.

Apart from its exotic appearance, for me there is one thing that sticked out: the 'panels' forming the head. If you take a look at the head you see a kind of panels that seem to be riveted together. Just like the plating of a ship is nailed together. If I am not mistaken, those formerly loose parts, nowadays one piece, are one of the characteristics of fish of prehistoric times.
Paleontologists trace this family back to the Devonian era, back 345 millions years. They belong with the sharks and rays to the cartilaginous fishes.

Nowadays there are worldwide approximately 35 species (Debelius, 1998). Most inhabit deep seas. That's why I thought at first sight: what are you doing in these shallow waters? But shallow waters are not uncommon for Hydrolagus, as for Chimaera monstrosa: Wheeler (1986): '...it seems that the ratfish migrates in unisexual shoals, large females being found in shallower waters in spring and summer... .'
And Betty Pratt-Johnson (2007) refers quite frequent to this ratfish, albeit several times while night diving: 'The eyes of ratfish glow like sapphires.'

She was about 75 cm long. The maximum recorded size is 97 cm. Why I think it is female (at least the one that came close)? Lamb & Edgell (1975): 'Males have an evertable projection on the head, that sits in a pit and is used during mating to grasp a female. Only males have claspers (sex organs).' I don't see a pit on the head of 'my' ratfish and no claspers near its pelvic fins.

The following day I saw them again; the same couple I expect. They showed no interest at all in that big man in black with all its preposterous diving gear.