56 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



IOh"" 



lOt"" 



Fig. 25. Primordia and cores of parrotfish sagittae. (A) Unidentified scarid larva, medial face up, core in focus. The dark crescent is a portion 

 of the crista on the surface. (B) Same as previous, but with increments in focus. (C) Suspected scarid larva, core in focus. (D) Same as (C), 

 increments in focus. 



incorporated into the otoliths. The mechanism appears to be 

 that the otoconia adhering to the otolith surface are surrounded 

 by new material accreting on the otolith, and eventually these 

 "included" otoconia are found deep within the otoliths of larger 

 fish. In some species, such as Anguilla rostrata otoconia are 

 found in dense bands corresponding to annual zones. "Includ- 

 ed" otoconia have only been observed in juveniles or older 

 individuals. 



Transitions in otolith microstructure involving changes in the 

 width and optical density of growth increments (Fig. 26) may 

 be related to a variety of morphological and eco-behavioral 

 changes in the early life history offish (Pannella, 1 980; Brothers, 

 1981; Brothers and McFarland, 1981; and numerous other pa- 

 pers; also related works by Postuma, 1974, and McKem et al., 

 1974). Hatching, yolk absorption, changes in feeding and hab- 

 itat, postlarval transformation, and settlement can all poten- 

 tially influence the deposition pattern of daily and subdaily growth 

 increments. To the extent that life history patterns consistently 

 diflfer between taxa, we may expect to find microstructural evi- 

 dence of events in the early life history which are of systematic 

 value. Difierences between taxa will then be expressed as dif- 

 ferences in the timing of marks (e.g., hatching) and otolith tran- 



sitions and in their intensity and duration. Thus we may use 

 otoliths to record ecological information which may then be 

 applied to systematic studies. An even simpler approach might 

 just be a quantitative comparison of growth rates as determined 

 from daily growth records (once validated, and the fish growth- 

 otolith growth relationships are known), however care should 

 be taken to avoid problems due to high intraspecific variability 

 in growth rate (e.g., Methot, 1981; Bailey, 1982; Brothers et al., 

 1984). Another possibility is the use oflarval life duration as a 

 taxonoinic character. There is evidence to both species speci- 

 ficity and very limited variability in some taxa, as well as vari- 

 ability or flexibility in others (Brothers et al., 1983; Thresher 

 and Brothers, in press; Brothers and Thresher. MS.; Brothers 

 and Erdman, unpublished), so caution must be exercised in 

 using this character as a taxonomic tool. 



A final ecologically related application is the determination 

 of spawning time (and perhaps place, by correction for current 

 drift) by age determination of larvae, with correction for the lag 

 between fertilization and increment initiation (Townsend and 

 Graham. 1981; McFarland et al., unpublished). When difl^er- 

 ences in spawning times are suspected or known to exist for 

 taxa, then larval age may be used to help in assigning identifi- 



