This is an old low, resolution slide scan of an adult tubemouth, Siphonognathus argyrophanes, likely being cleaned by some pencil weed whiting among the Posidonia under the eastern arm of the T-section of the old outer Rapid Bay jetty in around October 1992: –
(The photo is suggestive but not proof.)
I had forgotten about the likelihood that cleaning activity was occurring when I took the photo, along with several more. I’m sure I took more than one photo of this tubemouth, even though I was limited to 36 slide transparencies per dive, but I don’t know if I scanned the others. They are still stored in the original slide box so if I could get organised I’d love to dig out the box and review the other images. Feasibly one may show closer contact between client and host.
(Editor’s note – David has posted several tubemouth photos to iNaturalist – see https://inaturalist.ala.org.au/taxa/112704-Siphonognathus-argyrophanes/browse_photos , including the one further below. Several tubemouth photos also feature in the article Shrimps, Seadragons and Siphonognathus argyrophanes – Marine Life Society of South Australia Inc. (mlssa.org.au))
This photo also prompts a question for all of us, for which I doubt anyone knows the answer: – What are the preferred prey species for a mature tubemouth?
We know they’re specialist carnivores that are stealth predators (cryptic in and around edges of meadows, also able to alter from green to brown when hunting and hiding in seagrass detritus), and they are likely to be territorial to a degree, but I have no knowledge of their main prey species. It seems likely to be quite a broad range of smaller fish that share the same bottom type
e.g. Wood’s siphonfish, juvenile weed whiting of several types (Blue Weed Whiting and Longray Weed Whiting are 2 common examples), and perhaps adults of the smaller odacids e.g. Slender Weed Whiting.
Next question: Would they eat Pencil Weed Whiting?
Juvenile Pencil WWs are proven opportunistic cleaning hosts, but maybe adult Pencil Weed Whiting AND Tubemouths gathered as in the above picture could be clients of unseen grass clingfishes (long suspected by me to adopt host roles, but I’ve never witnessed it convincingly, let alone proven it with images).
Schools of juvenile pelagic scalefish (Blue Sprat, Pilchards, Anchovies, etc..) plus smaller groups of atherinids, e.g. Smallmouth Hardyheads, often swim above shallow meadows so are also common around meadows inhabited by tubemouths.
The design of this stealth predator’s mouth seems ideal for grabbing slender prey that are above the meadows or near the top of the seagrass blades. So gobies, blennies and other groups that are strictly benthic dwellers and often found on sand in or near meadows are probably not targeted by tubemouths.
Likewise, juvenile leatherjackets, while common in meadows, would be unlikely target prey, due their dorsal spine defence ploy. Juvenile tubemouths might feed mainly on mysids and shrimps ‘til they are big enough to take small fish.
All this is typical speculation of course.
But the tubemouth strikes me as being a fairly common thus key niche species of seagrass meadows throughout its range. So maybe MLSSA should look at collecting a few adults under permit, to examine the gut contents. (The alternative of collecting lengthy footage via fixed video cameras placed along the edges of healthy meadows would be more ethical, but require much more volunteer time, with no guarantee of successful ‘capture’ of feeding tubemouths).
With regards to analyses of gut contents, we’d need to liaise with local experts because I don’t think we’ve any current members who have the necessary skills.