Oreos—once bitten...

Figure 1. An X-ray scan of a spiky oreo.

This post is about oreos: the deep-sea fishes, not the cookies. I did wonder for a while which came first and perhaps that one was named after the other, especially since the eyes of some oreos actually look a bit like the cookies. Oreo means mountain in Greek and the Family name of the fish, Oreosomatidae literally means 'mountain-body'; referring to the large (dorsal) ridge found on the top of many species. As for the cookies, it turns out that oreo cookies were invented in 1912 and at one time were described as a 'mountain of a cookie', although apparently the history of the name is unclear.

Spiky oreo are a species of deep-sea fish (Neocyttus rhomboidalis Gilchrist, 1906, Family: Oreosomatidae), found off the coast of New Zealand and around the southern hemisphere at about the same latitude. Live oreos are not normally seen or caught by your average punter, as they are found between depths of 200–1200 metres. However, they are taken as bycatch in deep-sea fisheries, particularly those for orange roughy (Hoplostethus atlanticus, Collett, 1889).

There are commercial fisheries for black and smooth oreo and broadly speaking these fisheries are in similar places and depths as the orange roughy fisheries, although they tend to be further south. There are four common oreo species at these sorts of depths: black, smooth, spiky, and warty oreo. Spiky and warty oreos are the least common of the four and have a more northerly distribution.

For management purposes in NZ waters all four species are treated as one thing under the quota management system (Ministry of Fisheries 2014). I guess this makes it easier for the fishers, as they look similar. However, this is not so great for the fish themselves, as there is no way to know if one of the four species is being over-exploited if they are all recorded as the same thing.

Of the four species, the ecology of spiky oreo is arguably the least well known. Oreos have a gas-filled swim bladder and this expands rapidly as the fish is brought to the surface (a bit like the bends). As a consequence they suffer quite badly from stomach eversion; their stomach is forced inside out through the mouth by the expanding swim bladder (the expansion is caused by the change in water pressure and a particularly gruesome way to die I would image).

The only study I could find describing their diet recorded an eversion rate of ~94%. Lyle and Smith (1987) suggested that spiky oreo diet was dominated by zooplankton, particularly salps; although crustaceans,  fish, and cephalopods were also frequent food item. This is not a very helpful level of detail. However, this kind of diet suggests that spiky oreo feed in the water column and not from the seabed, which at least tells us something.

Anyway, I was going through some old photos the other day and came across a scan of a spiky oreo x-ray taken in 2004. These photos (Figures 1–3) are most interesting for the damage shown to the spine of this individual (Fig. 2). Predatory attacks on fish aren't always fatal, so I’m guessing this is either the result of an attack, or a malformation.

Figure 2. Note the repaired spinal damage.

Figure 3. A close-up of the dorsal spine.

Speaking of surviving attacks, Figure four is a picture of a warty oreo (Allocyttus verrucosus (Gilchrist, 1906)) with a large bite mark on it and Figure five is a close-up of the same bite mark. It’s not really possible to ascertain the size of the fish that made the bite mark, as the oreo may have grown since the bite. However, when the photo was taken the bite mark was about 50–60 mm across. I’ve been told that these bite marks are reasonably common and are often found in the same place—dorsally. The reasoning being that the oreos are not necessarily only being bitten in this area, but that bites elsewhere are fatal. I've not included data regarding the diet of warty oreo, as this is part of a paper I'm currently writing.

Figure 4. A warty oreo from Chatham Rise.

Figure 5. If you look carefully you can see the semi-circular scar.

This particular warty oreo was caught in 1062–1117 metres of water on northeastern Chatham Rise (same trawls as Jones 2008). I’m going to speculate that a deep-sea shark of some kind made the bite, as there are several likely candidates down at that depth. I wonder if it's possible to match the shape of the bite mark to a potential predator?


I'd like to acknowledge Steve O'Shea, as I think it was he who did the original scan of the spiky oreo. I honestly can't remember, but it seems a shame to not share the imagery, so I guess I'm doing it without permission. I'd also like to thank NIWA for retaining the fish for me; they came from the TAN0404 cruise.

References

Lyle, J.M. and D.C. Smith, 1987. Abundance and biology of warty oreo (Allocyttus verrucosus) and spiky oreo (Neocyttus rhomboidalis) (Oreosomatidae) off south-eastern Australia. Marine Freshwater Research 48: 91–102.

Jones MRL 2008. Dietary analysis of Coryphaenoides serrulatus, C. subserrulatus and several other species of macrourid fish (Pisces: Macrouridae) from northeastern Chatham Rise, New Zealand. New Zealand Journal of Marine and Freshwater Research 42: 73–84.

Ministry of Fisheries 2014. Oreo Fisheries Plan Chapter. ISBN: 978-0-478-43202-2 (online), pp1–53.