Recently I had a student working on a research paper detailing new species records for BC’s marine fishes. He examined Dreamers and Sea Devils – members of the deep-sea anglerfishes. These fishes have the distinctive bioluminescent lure hanging from a modified dorsal fin spine. In other words, these fishing fishes dangle a glow-in-the-dark lure to attract prey. There are at least nine species off our coast and they exist at depths from a few hundred meters to two or more kilometers. What do Dreamers and Sea Devils look like? Imagine a flabby, brown-black, round to pear-shaped fish with small fins, and a large mouth lined with needle-like teeth. Or how about a black elongate bottle-shaped fish covered in thorny prickles? One type of deep-sea angler, though not from BC, has the latin name Puck pinnata – and while the name conjures up thoughts of a candy-filled rubber projectile, it actually is based on Germanic folklore and its mischievous devils, sprites, goblins and demons. Another dreamer’s name translates to “pugnacious tyrannical toad”. But don’t be biased by their names, female dreamers and sea devils are among the most attractive of fishes and drift placidly in ocean currents.
This female Black Sea Devil, Melanocetus johnsonii (RBCM 014-00308-001) is the first of its kind from BC, from 865 meters in Father Charles Canyon (scale bar = 1 cm). The high number of dorsal fin rays (13-17) easily separates this fish from other local anglerfishes which at most have 8 dorsal fin rays.
This female Smooth Dreamer, Chaenophryne melanorhabdus (RBCM 999-00107-002) is in pretty good shape for a fish from a trawl net (scale bar = 1 cm). She came from 928 meters depth, west of Nootka Sound. Most specimens lose large patches of skin. Even the eye is visible just over a centimeter behind the attachment for the lure. The lure is made from two parts – the ilicium, (the fishing rod) and the esca (the lure). The esca is the main feature we look at to identify species even though it varies slightly within species. The pectoral fin and gill opening are obvious, and all fins were well-enough preserved to allow fin ray counts. We are not always this lucky. In some cases the lure is lost due to damage in the net, and species identification may be impossible without a DNA lab.
Male deep-sea anglers are tiny – they are all nose, eyes and gonad. Males serve only to swim and find a female, latch on, feed off the female’s body fluids, and mate when required. Males are a fraction of the weight of a female and look more like leeches or parasitic copepods than a fish. Many sources refer to these males as parasites on their respective females, but instead, they are reproductive slaves. In a parasitic relationship, the benefit is one-way – the host gets nothing out of the transaction. With anglerfishes, males gain nutrition, and both get reproductive reciprocation. At least female anglerfishes can’t complain that their mates are never around when needed. In some species at least, the male’s mouth completely fuses to spongy tissue on the body of a female and their blood vessels merge. Male anglerfishes give a new meaning to one of Lionel Ritchie’s signature songs. If male-female attachment does not shock you, then perhaps a 8:1 ratio of males to females will (8 males on one female is the record, although not in BC). Those females with more than one male essentially have a polyandrous hitch-hiking harem. On a multi-male-female, the first to attach is the largest. The smaller ones attach later. Males seem to attach along the belly of the female, and this makes sense for reproductive success. Towards the strange end of anglerfish biology (if it is not strange enough already), there is a record of a male Black Seadevil (Melanocetus johnsonii) which attached to a female Prickly Seadevil (Centrophryne spinulosa). Even in total darkness, you’d think the species would be able to recognise each other for something so permanent. The male’s motto should be, “Do, or do not. There is no try”.
Young male (M1) and female (F1) Northern Sea Devils can be distinguished at a young age; females already have the lure on the head and the caruncles (warts) towards the dorsal fin. The two genders grow radically different with the female growing its large capacious mouth (F2), and the male developing its pincer-like teeth and large eyes (M2). Males develop prickly skin by the time they permanently attach to their much larger mates (M3 and F3)(scale bars approximately 5 mm, image modified from Figure 3, Pietsch 2009, p. 7).
The larvae of Haplophryne mollis (modified from Figure 6, Pietsch 2009, p. 7, and also not from BC) remind me of a Lost Soul from the old video game DOOM 3. Nothing in science fiction or video games rivals the wonders of the deep sea.
This female Northern Sea Devil, Ceratias holboellii (RBCM 999-00081-001) was found at 419 m depth southwest of Barkley Sound, BC (scale bar = 1 cm). We now have four of these from BC and a single specimen of the Triplewart Sea Devil, Cryptopsarus couesii (RBCM 014-00309-001) from Esperanza Canyon.
Since none of our dreamers have attached males, we have to wonder why? Are males found farther south? Are they able to release seasonally? Can males drop when females are stressed in a trawl net? Elsewhere, females have been caught with males attached, so it is unlikely males bail out when a female is in peril. But only a small proportion of females are known to have attached males. If that is a true reflection of their biology, then as Ted Pietsch suggests, a population’s success could hinge on very few breeding adults.
Reproductive success in these fishes is a big mystery, although large females can carry a few million eggs, and reproductive maturation is stimulated by the attachment of a male. Given the depths they inhabit, we may never get a good handle on their breeding biology, but what we know is summarised in Ted’s book. I suppose deep-sea anglers are fortunate that we don’t harvest Dreamers and Sea Devils at the rate we harvest other species. If the reproducing population is indeed a fraction of the total population, the loss of a few breeding females would be catastrophic. They’d also cost a mint at the grocery store, since a deep-water trawl may only get one every few days – and ships cost thousands a day to operate.
This female Smooth Dreamer, Chaenophryne melanorhabdus (RBCM 998-00323-001) collected by Graham Gillespie (DFO) from 1036 m between Nitinat and Barkley Canyons, obviously had eaten a large meal. Curiosity got the better of him, and Graham opened the gut to find this wad of packing tape (scale bar = 1 cm).
You’d think our deep sea environment would be somewhat pristine, because we visit it so rarely. But even deep-water fishes wallow in trash, even before the tsunami debris headed east after the Tōhoku Earthquake. Our trawl samples have hauled up boots, shoes, beer cans, and even a child’s skipping rope far west of our shores. Like albatross that ingest shiny plastic only to feed it to their young, the Smooth Dreamer with a wad of packing tape is ample reminder that we need to be more responsible with garbage. I wonder if the person who threw the tape overboard had a clue where it would end up? This female’s days were numbered. With this obstruction in her gut, she’d have starved to death. Normally deep-sea anglers feed on fishes, but also take cephalopods, amphipods, ostracods, polychaete worms, gastropods, cnidarians, and sea urchins, and very likely eat smaller compatriots when the trawl net is hauled to the surface. Be suspicious of any “fresh” items in an anglers stomach, it may be a case of net-feeding. In turn, deep-sea anglers are eaten by fishes such as tuna, Black Scabbardfish (Aphanopus carbo), Longnose Lancetfish (Alepisaurus ferox), and the Deep-sea Swallower (Saccopharynx lavenbergi). It’s unfortunate that the eyes of males degenerate once attached to a female – they could serve as a rear-turret to detect approaching predators. Even Sperm Whales are known to eat deep-sea anglers, but I can’t imagine a whale will get much energetic gain from a single dreamer. Perhaps animals with bioluminescent parts are a whale’s way of “eating light”.
Do you want to know more?
Pietsch, T.W. 2009. Oceanic Angler-fishes: Extraordinary Diversity in the Deep-sea. University of California Press, Los Angeles. 557 p.