Fish otoliths: do sizes correlate with taxonomic group, habitat and/or luminescence?

Otoliths are dense structures in the cars of fishes: that function in heari ng and gravity; perception. Otolith (sagitta) diameters, as percentages of standard length (% SL), are calculated for 247 marine fish species in 147 f amilies and compared by taxonomic group (usually order), habitat and presen ce or absence of luminescence. Otolith sizes range from 0.4-31.4 mm and 0.0 8-11.2% SL. The ed and spiny eel orders Anguilliformes and Notacanthiformes have small to very small otoliths, as do the triggerfish order Tetraodonti formes, pipefish order Gasterosteiformes, billfish suborder Scombroidei and many of the dragonfish order Stomiiformes. The solderfish order Beryiforme s has moderate to very large otoliths. The perch order Perciformes has a wi de range of otolith sizes but most have small to moderate otoliths 2-5% SL. Only 16 out of the 247 species have the relatively largest otoliths, over 7% SL. Seven out of these 16 species are also luminous from a variety of ha bitats. Luminous species have slightly to much larger otoliths than non-lum inous species in the same family Both beryciforms and luminous fishes live in low-light environments, where acute colour vision is probably impossible . Most fishes of the epipelagic surface waters have very small otoliths, pe rhaps due to background noise and/or excessive movement of heavy otoliths i n rough seas. Bathypelagic species usually have small otoliths and regresse d or absent swimbladders. Other. habitats have species with a range of otol ith sizes. While the relationship between hearing ability and otolith lengt h is unknown, at least some groups with modified swim-bladders have larger otoliths, which may be associated with more acute hearing.