Oncorhynchus mykiss

Rainbow Trout at Cotter River, ACT

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Identification history

	Oncorhynchus mykiss	17 Oct 2023	MattBeitzel
	Galaxias sp. (genus)	17 Oct 2023	Ct1000

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User's notes

Probably a stretch to get a specific species especially with a phone photo. Tail had a golden /red colour. Black stripes or barring down the sides.

8 comments

MattBeitzel wrote:

17 Oct 2023

Its a juvenile Rainbow trout by the par markings and the fin alignment. Lack of a red tinge to the adipose fin indicates its not a brown trout.

Ct1000 wrote:

17 Oct 2023

Ah a shame. But definitely makes sense at that location

MattBeitzel wrote:

17 Oct 2023

Yes it would have hatched at the end of august. There are galaxias in that catchment but not usually where the trout are. There are native fish at that location if your quiet and careful.

Ct1000 wrote:

18 Oct 2023

Yeah I believe I saw a two-spined black fish there last year sometime but didn't get a photo. But definitely in that location both trout species seem to be the dominant species. Do you know anything about shrimp? That night on the weekend was the first time I didn't manage to see any shrimp (the glass shrimp species paratya) at that location on a night visit and I was wondering if I just didn't see them or the deeper water, seasonal change or some other factor might be effecting their numbers there.

Ct1000 wrote:

18 Oct 2023

Also what kind of fin arrangement helps differentiate between galaxias and trout at that size?

MattBeitzel wrote:

18 Oct 2023

Galaxias only have one fin on their back and its situated well to the rear, overlapping the anal fin. This has a dorsal fin more to the mid section of the body and there is an adipose fin (a small thumb shaped fin) on the caudal peduncle (fleshy bit in front of the tail) on a fish this size the adipose its pretty small but you can see it in the photo. The fin on the underside under the dorsal isnt the anal fin its the pelvic fin and it should be paired but that cant be seen in the photo. For a phone photo in the water its pretty good for such a small fish. If it were a galaxias the only back fin would start about where the dorsal on this fish ends. As far as we know from genetic analysis all ACT galaxias are G. olidus. and we have a pretty broad sample across the ACT.

MattBeitzel wrote:

18 Oct 2023

Blackfish and Macquarie perch are pretty common at that location. Shrimp are difficult to work out what causes peaks in populations as some years there are tonnes of them but I wouldn't expect them to be particularly common coming out of winter.

Ct1000 wrote:

18 Oct 2023

Thanks so much for all the extra info!

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