All measurements were made with an eyepiece 

 micrometer and a stereoscopic microscope and re- 

 corded to the nearest 0.01 mm. 



MEASUREMENTS 



Measurements used when working on larval flat- 

 fish require definition, because they differ signifi- 

 cantly from those used on adult flatfish. 



Standard length (SL) : Tip of snout to that point 

 on notochord where dorsal flexture takes place 

 (dorsal and anal finfolds have a slight inden- 

 tation where the notochord turns dorsally, ac- 

 tinotrichia are visible in the caudal region of 

 the finfold immediately posterior to this in- 

 dentation) ; or tip of snout to base of median 

 caudal fin rays if these rays are developed ; or 

 tip of snout to distal end of hypurals if cau- 

 dal fin rays are developed. 



Head length (HL) : Tip of snout to posterior edge 

 of cleithrum on a horizontal line through cen- 

 ter of left eye on small larvae ; or tip of snout 

 to origin of dorsalmost part of pectoral fin 

 base ; or tip of snout to posteriormost part of 

 opercle on large larvae. 



Body depth (BD) : "Wlien left side pelvic fin base 

 is not developed, vertical depth is taken im- 

 mediately posterior to the cleithrum ; or from 

 origin of left side pelvic fin base to dorsal 

 margin of body (excluding finfold or rays). 



Origin of pelvic fin base to cleithrum : Least dis- 

 tance from origin of pelvic fin base to ventral 

 tip of cleithrum, both left and right sides. 



Eye diameter (ED) : Horizontal distance across 

 the left eye. 



Upper jaw length (UJL) : Anterior tip of pre- 

 maxillary to distal edge of maxillary. 



Lower jaw length (LJL) : Symphysis of lower 

 jaw to posterior edge of angular. 



Snout length (SN) : Anteriormost part of pre- 

 maxillary to anterior edge of left eye. 



COUNTS 



Dorsal, anal, caudal, and pelvic fin rays: Total 

 number of fin rays in which the basal portion 

 is distinguishable. 



PROBLEMS ENCOUNTERED IN WORKING 

 WITH LARVAL FLATFISHES 



The wide variation in measurements and counts 

 of larval flatfishes may be due to distortion by 



preservation or to differing rates of development. 

 When killed and preserved the larvae often curl; 

 the pectoral fins may harden in an extended posi- 

 tion ; the mouth may open and distort some head 

 features ; and the eyes often distend, shrink, or fall 

 out. Larval fish are fragile, and fin rays are often 

 broken, particularly the elongate rays. Poor pre- 

 serving and collecting teclmiques often damage 

 or distort specimens. Fresh, well-preserved, flat- 

 fish larvae can be held in place for examination 

 by a cover slide, but older, softer, or poorly pre- 

 served material may be damaged if handled in this 

 manner. Older, softer specimens are often difficult 

 to measure; however, they are often partially or 

 completely bleached, so that tlie fin rays and myo- 

 meres or vertebrae are easier to count than in the 

 fresh firmer specimens. Much of the material from 

 the Theodore N . Gill is soft, but that from more 

 recent Oregon cruises is in excellent shape. 



Pigment patterns fade and are lost in preserva- 

 tive, so a knowledge of wlien specimens were col- 

 lected is important; also the rate of development 

 is not the same for all individuals. Larvae col- 

 lected over a wide geographic area and an ex- 

 tended period of time may show differing rates of 

 development. Within a species, fishes that meta- 

 morphose at small sizes probably liave different 

 rates of development from those that metamor- 

 phose at larger sizes. These differences must be 

 recognized when working with larval flatfish. 



CHARACTERS USEFUL IN IDENTIFYING 

 BOTHID LARVAE 



Characters that can be used to identify bothid 

 larvae fall into two categories: (1) transitory, 

 those which are present during part or all of the 

 larval period but eventually are lost and (2) per- 

 manent, those which develop during the larval 

 period and are retained in the juvenile and adult 

 stages. 



Transitory characters include larval pigmenta- 

 tion, elongate fin rays, and head and body spina- 

 tion. Type and intensity of these transitory char- 

 acters may be of generic or specific significance. 

 Many of the bothid genera in the western North 

 Atlantic have elongate dorsal and pelvic fin rays 

 in the larval stages: Paralichthys (Hildebrand 

 and Cable, 1930) ; some Citharichthys (Ahlstrom, 

 1965; O. stigmaeus has no elongate dorsal fin 

 rays) ; Syacium (Aboussouan, 1968) ; Bothus and 



LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER 



265 



