I have seen people use ultra-sound to check the size of the gonads... I believe it is actually fairly common in the production of sturgeon for caviar...

Depending on the size of the fish, you could use a pipelle, or canula, to do an intra ovarian biopsy:

http://www.anfo.nl/file/f052_pipelle_brochure.pdf

https://www.thomasmedical.com/sites/default/files/files/Pipelle_de_Cornier_Package_Insert.pdf

We developed an ELISA for VTG and used it to detect maturity in the surface mucus of adult female striped bass. It was 100% correct. My pubs for vitellogenin are listed on this site. Good luck.

I was marginally involved in a study for non-lethal sex id in billfishes, using ELISA technology, but we never experimented for maturity.

Below is the reference, you may find something new nowadays, but I'm not aware.

Reference: Schultz et al. 2006 Bulletin of marine Science 79 (3):859-864.

good luck.

I have used a simple lightbox to estimate ovary size in female flatfish. Methods described in Kennedy, J., P. R. Witthames, R. D. M. Nash, and C. J. Fox. 2008. Is fecundity in plaice (Pleuronectes platessa L.) down-regulated in response to reduced food intake during autumn? Journal of Fish Biology 72:78-92.

Yes I saw that, but I think there is quite a bit of work involved in that. I was thinking more along a test of a swab for hormone or something like that?

Not a lot of work if you just wanted to categorize individuals as mature/immature - this could be done by eye. But I'm pretty sure it won't work for males or non-flatfish, so it sounds like a hormonal approach would be better. Good luck!

Would be useful to the audience to know your target species and environment. Are they marine or fresh water fish? What season for proposed sampling will also impact results.

If you take some plasma from blood samples you check hormone levels. We did is with clown fish and sharks:

Mills SC, Mourier J, Galzin R (2010) Plasma cortisol and 11-ketotestosterone enzyme immunoassay (EIA) kit validation for three fish species: the clown anemonefish, Amphiprion percula; the orange-fin anemonefish A. chrysopterus; and the blackfin reef shark, Carcharhinus melanopterus. Journal of Fish Biology 77(3): 769-777.

A lot depends of the species, and on what you consider "mature"

There are some things (e.g., size of the fish) that will determine whether or not this is possible, but I recall that in aquaculture, a catheter is used to extract tissue from gonads so that the stage of development of gametes can be determined. Additionally, in later stages of gonad development, it is possible to produce milt and roe by gently pressing on the abdomen.

There is some literature addressing non-lethal approaches in sharks. You may want to take a look at Awruch et al. (2008) Non-lethal assessment of reproductive characteristics for management and conservation of sharks. Marine Ecology Progress Series, 355: 277-285. Good luck!

Wish I had a more complicated answer but essentially size is a reliable determination of developmental stage especially in early life history.

If you let us know the species, we could be more helpful, and are you looking for reproductive seasonality or just mature/immature state? Hormone assays are complicated by hermaphroditism in some species, and the level to which assays work differ between elasmobranchs and teleosts....and even between species. I think the likely answer to your question is that there is not a cheap and easy method for most species.

http://www.sciencedirect.com/science/article/pii/S0044848608002044

Dane Newman used ultrasound to determine maturation stages in Murray Cod. The method may be useful in other large species. Inexpensive! I have provided the link to one of his papers.

It depends on the species you are working with. If you have data of the average size of first reproduction for each sex you could have an idea wether each individual you capture might have reached maturity or not just by measuring their standard lenght. This is very advantageous because you could estimate it even if you are not sampling during the species reproductive period, and it is easy and cheap.

If you are sampling during the reproductive period you could massage the fishes to see if they expel eggs or sperm. But honestly you will obtain more accurate data by sacrificing a few ones to examine their gonads.

If hormonal tests etc. are unavailable, and you could freely choose sampling time, you could simply do the sampling during the spawning time. Then both external, secondary sex characters may be easily visible, at least for species within some families, and for males, running milt may additionally reveal their sex

The fish maturity status depends on many factors such as age, temperature, exposure light hours, feeding quantity and quality and even the presence of each sex with the other. Sex hormones secretion affected by these factors. In the reproductive season, you can detect the maturity of fish by the presence of eggs and sperms by light pressure at the lower area of the abdomen from the head to the tail (stripping). Also in tilapia, the lower part of male jaw will colored in red and begin in the courtship behavior.

Wow, so many answers! I'll browse these through the week, Thankyou. For now I can add it is European perch and pike and I am looking for signs of first year of reproduction.

Males will usually express milt with gentLe pressure, females are not so easy. The cortisol test sounds interesting.?

T

Hi Tom.

Don't bother with ELISA tests. It's useless. Sexual hormone concentrations are too variable to distinguish males from females with a 100% chance. Even 11-KT assay during gametogenesis is not reliable, neither for perch or pikeperch. Cortisol is not a marker of gametogenesis or reproduction. The best method will be the catheter method. I think it will roughly work from January to April. However, I'm not sure that you can say that it is not invasive. You'll need someone with experience because you can easily harm the fish. The rest of the year, it's impossible to ascertain the sex of those fishes without killing them. Trust me.

In any case, the catheter method will allow you identifying some males and females undergoing gametogenesis (positive reponses). But a negative response (nothing in the catheter) won't allow you concluding that the fish is immature with 100% certitude.

Question: at which period of the year do plan to sample the fish ?

Even lethal and labor intensive methods can be unsuccessful for distinguishing mature from immature individuals, like gonadal histology. The main problem is that immature fish have the same composition of gametes with regressing, resting or very early regenerating fish (all these are mature phases): females from all these phases contain only primary oocytes. Therefore, simpler indices like the gonosomatic index or the macroscopic appearance of the gonad should again be unsuccessful. Some workers use other characteristics like ovarian wall thickness or the prevalence of atretic follicles. Blood tests for steoid composition (e.g. estradiol levels) could be one possible solution but then your method will not be simple any more. These difficulties make simple and non-invasive tests for the maturity status almost impossible.

I fully agree. For immature fish or fish with freshly started gametogenesis, histology is mandatory. With the exception that in Eurasian perch, it is very easy to distinguish male from female gonads by sight, because the ovaries are fused. This does not apply to pikeperch.

Thank you for so many answers. We have multiple sampling of these perch. We have four populations and we sample in May for mark-recapture and we know these are mostly mature fish as they are attracted to the traps at the edge of the lakes to spawn, just after the ice-break of the lakes. And we can express milt from males by this point, and it is likely most females are mature. But I wanted to expand our method of catching to try and find a mixture of mature and immature fish, as it was specifically that variation I am interested in, but not kill them. As it happens we also have a fixed effort multimesh gill-net sample in late July which we use for growth rate estimations and from this year a lethal size-structured harvest.... but of course by them the gonads are all retracted. It seems ultrasound is the only likely candidate and I think that may be too much work in the field on top of what I am already doing :0(

we have fish that have been growing in our facilities from same cohort and breeding season but their sizes are different (we don't have room to size grade) but when I open some of the fish up after dying from different reasons I noticed that some of the fish despite being same size have different maturation stages i.e. the testes were not same size and the females have eggs at different maturation stages and sizes. so waiting until the breeding season comes is the best way (cheapest if you are willing to keep them and feed them) in tanks

Hi Tom,

In some marine fish like cod, we have used biopsy pippettes (like this ones http://www.globescientific.com/open-end-pipettes-c-28_478.html). We introduce them by the gonopore and take a small biopsy of the gonad to do histology. As K. Ganias has said, histology has some limitations, especially if you are sampling out of the spawning season, when immature and regressing/regenereting females could be together. The pippetes are very useful if you are working with robust fish species, for example, in hake that is very sensitive to handling, they cannot be used.

If you want to use this method, try it before in some dead specimens (to test the method and train your ability) and after try it with live specimens.

I hope it will be useful.

I'm not sure that it is very ethical to handle wild fish like this. As I said, you have to be skilled to use these techniques. Otherwise you may injure the fishes, that may not be able to further reproduce. If you sample a lot of them, it could be detrimental to the population.

Hi Tom

I have never worked with your species but with my marine percid fish I found that the tissue swelling status or reddish coloration of the cloaca in females is a good indication that the fish are ripe or spawning ready vs immature females with no tissue swelling or reddish coloration of the cloaca.

Maybe this fast and non-invasive method can work for you.

Tom,

Don't give up on ultrasound so quickly. We use it for captively reared salmon. It's pretty quick and we get 90+% accuracy in April (four months ahead of spawning) and nearly 100% in May. Females are more obvious than males. It sounds like you're going to use it during the spawning season and, since both sexes should be obvious at that time, it should be a very quick process.

...reddish coloration around the throat of tilapia oreochromis niloticus often indicates maturity and  readiness to spawn

Timothy, can you supply as detail and resource info on how to use ultrasound and where to procure equipment for this purpose?...

sorry to have been missing these, was moving house, I'll catch up soon

HI all, it appears to me that the only non-invasive way to try this would be ultrasound. I have all the easy cues recorded (swelling of cloaca in females and milt of males), but beyond that the hormonal or biopsy methods are not for me :0) This has been a great discussion and thankyou for all your help

T