Lets assume they are the same species (because according to the identification guide based on morphometric and meristic counts the species are the same) is there are a line of thougth or theory to support the difference in the shape of their otoliths based on growth rates?

hi,

Well otolith shape has been used as a stock identification parameters in many exploited marine fishes. So just look into Stock discrimination problems in North Atlantic herring, Atlantic cod and others and you will see that the otolith shape is likely to tell you something about population structure within the same species.

Forgot to say that it is no necessarily linked to differences in growth pattern...

There is, at least, a plausible functional mechanism implying natural selection. Otholiths are usually bigger in demersal and benthic fishes than in pelagic species. This is probably due to the need for a fine sense of accelaration, needed to be able to move efficiently or quickly change directions of movement in a more heterogeneous habitat (think about obstacles and hides, small caves, rocks, gorgonians, corals, etc. of benthic environments as compared with open pelagic ocean).

Thus, if two different populations of the same species (one benthic or demersal and the other more pelagic) (what is indeed weird enough for fishes!) would have independent mating systems (that is, they are not panmictic), at least in theory, adaptative genetic differences between populations could arise by natural selection.

Growth rate does affect the dimensions (size) and the weight of the otolith. Different populations of the same species that differ in their growth rates will therefore have different otolith size for the same age. In general the slower growing population will have thicker and heavier otoliths.

Hi colleagues,

I came around some literature recently on the use of otolith shape descriptors to discriminate fishes of the same species based on feed intake and growth rate. They reported that the effect of feeding regimes was evident in the otolith shape even in as short as 30days. They further stated that the more roundish otoliths indicated increased growth rate while the the less roundish indicated otherwise for that species.

Are there any contrary views? I could upload the paper if u wish.

@ Owen is it possible for a species to be either pelagic and benthic a depending on habitat? For instance catfishes are not adapted for pelagic life.

Right! That's why I wrote "indeed weird enough for fishes!" in my comment. The pelagic and benthic realms are too different, But anyway, you could find some cases of generalist species able to thrive in demersal habitats with different degrees of complexity. I'm thinking about some sparids or some gadids, which could be able to live in different benthic/demersal habitats (rocky/sand/mud bottoms, for example).

I came across this publication i guess it provides some explanations.