Thanks Usman; do you have any data evidence to support this? It sounds plausible, something I've considered too, and looking for publications to support this or alternative hypotheses

Barramundi (Lates calcarifer) are a good example of diadromous fish in Northern Australia. It is common for barramundi to become 'land locked' in far upstream freshwater pools under seasonally dry tropical conditions. If drought or poor monsoon rainfall then fails to create sufficient river flow, the connections of these fish to saltwater environments for spawning activity can be temporarily prevented. Barramundi will persist in such upstream freshwater environments for extended periods (as they do when stocked in freshwater impoundments/dams).

Here's a link to an article which may be of interest.

Article Movements of Diadromous Fish in Large Unregulated Tropical R...

Thanks for the email Dr March. I work at JCU in northern Queensland and know Barramundi very well. Thanks for the reference, I'll follow that one up.

Thanks Nathan

I work mostly with salmonids that are, I guess, optionally diadromous. Pink Salmon, which always mature in the ocean in their native range, have adapted to life in the NA Great Lakes when stocked there once. Some species, such as Cutthroat and Rainbow trouts, move between fresh and salt annually. The "pattern" is spawn in fresh, incubate and rear in fresh, mature in salt, and return to spawn (numerous times). Within this, I have seen fish return from salt, overwinter, go back to salt (swim across estuary) and go up another stream within a few days. Others may spawn, and then stay in fresh for a another year. Long way of saying that the diadromous fish are (probably) very adaptable and responsive to local conditions.

Thanks Hal, how truely bizzarre. This is my point, are fish we think are diadromous having to adapt to a new world and therefore don't require this migration. Have you any published data on your observations?

I can try to find the cutthroat paper; it was done on paper but I'll see if I have a pdf. Just Googleing "Great Lakes Pink Salmon" should describe what is going on there. Tom Quinn's book (American Fisheries Society) on Pacific Salmon should have a good discussion on movement between saltwater. The older book, Pacific Salmon Life Histories, should also cover the topic generally. Lots of the knowledge is just accumulated. For example, salmon go to the ocean at a certain size. Yet, we can put them directly into saltwater at significantly smaller sizes and they do well. Conversely, resident Sockeye Salmon (Kokanee) apparently retain the ability to survive in saltwater even though it has been millennia since they were actually in it. The fish may (do) have a preferred life history but are apparently able to adapt to disruptions.

Gerry Closs has been exploring this same phenomenon has he not? Landlocked Galaxias populations?

Thanks Danswell, I'll contact Prof Close for any further leads. How are things down you way?

Nathan Waltham Im good mate. Working on water quality and catchment processes related to water quality and quantity these days.

I have a typical guide specia examples of Diadromus fish, Mugil cephalus, Liza auraqta and Liza ramada, and partli Coptodon zillii. We have published a lot about it, see in the newly (2018; Author: Prof. M. Gophen) published book entitled "Ecological Research in the Lake Kinneret and Hula Valley (Israel) Ecosystems" Sientific Research Publishing.

Fantastic, thanks Moshe and Jan for your input, I will follow up these literature sources.

In NZ we have a lot of species which are amphidromous, so head out to sea as soon as they hatch and return after 3-6 months. This is the most common type of diadromy found on tropical islands too. Almost all amphidromous species in NZ have now been found to be able to recruit from lakes, wetlands, or perhaps slow-flowing large rivers rather than the sea - we think as long as there is suitable plankton to support the small larvae. It seems only a few species - particularly the Sicydiine subfamily of gobies common throughout the Indo-Pacific - absolutely require entry to seawater to develop. A lot of the diadromous shrimp species also seem to require entry to seawater to moult to first feeding stage and survive

http://www.publish.csiro.au/mf/pdf/MF16387 this paper discusses some of our stuff in NZ and could be worth a look.

Hi Nathan,

In addition to Matt's recommendation you may be interested in this paper which concerns directly Australian gobies with facultative diadromous migrations:

https://onlinelibrary.wiley.com/doi/10.1111/fwb.12373

There is also a growing number a studies describing facultative diadromy in freshwater eels including tropical ones. See for example:

https://www.researchgate.net/publication/257509563_Migration_and_habitat_use_of_the_tropical_eels_Anguilla_marmorata_and_A_bicolor_pacifica_in_Vietnam

Raphaël

Hi Nathan. Interesting pondering. What species was it and how well do we know it's biology? I recently heard a talk from David Cook in the NT and it questioned a few of the assumed migratory traits of Barra that challenge the long held simplistic model of catadromy for them. This species you observed might not be that well known and has a more flexible strategy than first thought.

A few questions i had relating to your observation. How juvenile was the fish. Could it have been a slow grower from last season? Are you confident there has been no connection, thus it could be just a lucky one to get upstream in the dry season low flow.

What is really necessary will be to have marked fish that are persistently observed. We "know" that Pacific Salmon (the original species, not the recently added trouts) go to sea as juveniles, return to freshwater, spawn, and the die. Except, up in Alaska they marked some coho salmon smolts as they left the stream in the spring. That Fall, one entered a separate watershed, overwintered, and left for the sea the next spring. The next fall, it entered a third watershed and overwintered and left for the salt a third time. When we can mark/tag and follow fish, rather than having to kill them to read the tag, we learn a lot.

Hi Nathan,

You might be interested in looking at some of the literature on amphidromous shrimps. There are populations of Macrobrachium amazonicum in large South American rivers where the populations closely connected to the sea retain an obligative amphidromous life history, but those populations too far upstream to ever migrate to the sea can now complete their life cycle fully in freshwater. Klaus Anger was investigating this species. My paper Article Importance of the natural flow regime to an amphidromous shr...

Cheers

Peter

To piggy-back on Peter's answer, the Pacific Salmon (Chinook, pink, chum, sockeye, coho) are generally considered to be anadromous. The sockeye have populations that are naturally resident (kokanee) but the other 4 have, to my knowledge, no naturally resident populations. Those 4 all have man-created resident populations, some of which are now self-sustaining. The rainbow trout has some sort of internal mechanism that responds to environmental conditions and either stays in freshwater or goes to salt. Migration between fresh and salt is obviously very complex; I think many species have the capacity but not the behavior. On the other end of the scale we have some flatfish (supposedly marine) that utilize the lower reaches of streams; they may be in a low-saline environment. Just remembered that some of our sturgeon will move upstream, from the salt, on annual feeding runs where they consume salmon carcasses, eggs, etc. And then go back.

Hi Nathan,

"Caspian trout Salmo trutta caspius has listed as an endangered species according IUCN. It is an anadromous forms of brown trout that inhabits the southern part of the Caspian Sea which migrates mainly to the rivers during early autumn for spawning after smoltification followed by migration to the Caspian Sea."

It also might be interested for you "The evolutionary consequences for seawater performance and its hormonal control when anadromous Atlantic salmon become landlocked" by Steve McCormick et al 2019:

Article The evolutionary consequences for seawater performance and i...

Best regards,

Salman

Hello Nathan and colleagues,

I believe the comprehension of individual migratory patterns in fish has changed along the past 20 years or so. Today we know that many called “anadromous fish species” present in their populations some fish that (1) do not migrate and (2) migrate differently than expected. The reproductive success of these alternative migratory strategies, however, is quite hard to figure out. You may find a lot of information if you search for otolith chemistry + fish migration. Best wishes!

If I understand the question - you are wondering how diadromous fishes could exist in a system without a stream connection to the sea. The are many examples of ecotypes of diadromous species in the salmonid family that have versions who remain in freshwater either with or without a sea connection. Examples include Kokanee a freshwater form of the Sockeye Salmon (Oncorhychus nerka), landlocked Arctic Charr, Salvelinus alpinus, Broad Whitefish, Coregonus nerka and Inconnu, Stenodus luecichthys. Another alternative is that there is a connection to the sea that you cannot detect either through an underground stream or as we noted in our studies of Arctic Charr on Baffin Island, the fish might be moving up and down an apparently dry stream when there are high tides. Ross

In Lke Kinneret the situation is more complicated:marine species are removed from the Mediterranean and stocked in freshwater lake

Ptesently results are great success: beneficial for both: water quality and fishery income improvement