I assume you are using Nancy Auer's guide. The fish looks like it has to be a percid. Have you tried ruffe (Gymnocephalus)? Auer did not cover this species but European literature says ruffe have a low myomere count and only two myomeres between the yolk sac and gut, which I see on your picture. Also ruffe are supposed to be in Green Bay. Let me know if this works.

Drewry's punch card key to ys larvae puts this into centrarchids, according to your picture and info - there's a description of ruffe, which suggests a larger larva:

SIMONT, . P., and VONDRUSKJA. T, . 1991. Larval identification of the ruffe, Gymnocephalus cernuus (Linnaeus) (Percidae:

Percini), in the St. Louis River Estuary, Lake Superior drainage basin, Minnesota. Can. J. Zool. 69: 436-442.

If this is a centrarchid, it has to be Lepomis. I do not see the "Lepomis spot" on hindgut dorsum on the picture nor do I see the line of ventral melanophores on the tail that is typical for Lepomis. Also Lepomis larvae tend to have small and posterior oil globules whereas this specimen has a large ventral one. I have no access to the ruffe description that Audrey mentions, would love to have a copy!

Does not look like ruff:

https://www.researchgate.net/publication/230718968_Early_development_of_three_Gymnocephalus_species_reflections_on_the_evolution_of_the_genus

Article Early development of three Gymnocephalus species: reflection...

Oleksii, thank you for the paper. It is very useful. I agree that the picture does not look like a ruffe. Marian, it looks like you have other specimens. Is it possible to take a picture of several in one frame?

If you have sample please go for COI barcoding to know the species. I think it is a family: gobidae fish larvae

The timing, size, total myomere count, and wide/jagged myomeres are very morone-esque. Did you catch many?

Morone hatches at a smaller size and has an anterior oil globule. I am more inclined to consider it Aplodinotus or perhaps a centrarchid.

Hi all,

this is definitely not any Gymnocephalus species (the number of myomeres is much higher), and I even do not think it is a Percid. I would go on searching in the other families.

All below in reference to Auer. (1982) and a handful of loose-leaf materials.

The oil globule in the yolk sac seems positioned like I'd expect of Aplodinotus, but I wouldn't expect it to be so obviously persistent in this size drum.  Also, I wouldn't expect a drum to have so much pigment in the eye at this size and so little evident on the head or dorsal surface of the gut.

Vent position relative to both body length and yolk (seems to anterior for Morone spp. or percids), visually evident myomeres (or very close), size with yolk sac presence , etc. would seem to imply an early hatched Lepomis.  Lepomis spp. aren't necessarily pigmented at hatching.  However, I would expect any evident oil globule in Lepomis to be close to the posterior edge of the yolk.

Without seeing more or better detail, my initial reaction might be Lepomis in spite of the one anomalous feature.  I might waffle to Aplodinotus with more detail.

Hello all,

Wow, thank you all so much for your incredible wealth of knowledge and input. I am attaching a few more detailed images of the larvae in question. Note that they have a posteriorly-positioned oil globule and very light pigmentation beginning on the anterior portion of the yolk sac as well as above the eyes. In this particular bongo tow, I collected approx. 2,300 larvae that looked like this. Thank you again for all of your input!!

Marian

Thanks for the new pictures, very helpful I think..

Sorry for the long response:

Percidae- The only one I thought possible was ruffe, but my European colleagues are much more familiar with this species and they are right that your larvae cannot be ruffe. So, Percidae is out.

Moronidae- The only moronid in range is white bass (M.chryops). Moronids hatch very small and by 4.3 mm should  not have a yolk sac. White bass YS larvae have the head over the yolk sac, not free as in your specimens. Other moronids are out of range and have very similar appearance to white bass. I suggest that your larvae are not Moronidae.

Centrarchidae- Lepomis would be the only genus that is reasonable, all other centrardhis in range have massive guts. I don't like Lepomis for your specimens because 1. There is no "Lepomis spot" on dorsum of gut. 2. At that size Lepomis have pectoral buds and I don't see that on your pictures. 3. Oil globules in Lepoms are rather small, the globule on your specimens is huge.

Sciaenidae- Freshwater drum (Aplodinotus grunniens). This species is recorded from Green Bay. If you compare your specimens to Auer, the size is correct for yolk sac larvae, the size and location of the oil globule works. Auer does not give myomere counts for yolk sac larvae but counts from her illustrations are close to yours. So, I vote for freshwater drum. If you have a large series of these larvae you could do the world a favor and publish a detailed description.

I work in the Hudson River and drum are becoming abundant. If anyone knows of a published description of the larvae other than Auer, please let me know!

Marian, 

I agree with Robert & Eugene, my initial reaction was Lepomis but it lacks the spot on the dorsum & the globule is gigantic. My vote is also Aplodinotus; which makes since for the assemblages of Green Bay.Hope all is well. 

I am still inclined to consider these larvae as Aplodinotus. The body size, oil globule, pigmentation, and myomere counts are consistent with what's in the literature. A comprehensive account, complete with illustrations and descriptions of the developmental series is available in: R. Wallus and T.P. Simon, "Reproductive biology and early life history of fishes in the Ohio River drainage," Volume 5, CRC Press. If anyone is interested in a copy of this, or the relevant part of a book chapter on Freshwater Drum that I am working on, feel free to contact me ([email protected]).

Ed Rosman at USGS in Ann Arbor ( https://profile.usgs.gov/eroseman) does a tone of Larval work on the Great Lakes. You could shoot him an email with your images.

Hi, I would like to ask, what is reference you used (what books or article) for the identification of fish larvae?