214 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



is very seldom encountered, however, because of 

 damage to the arch, destruction of rakers by 

 parasitic isopods, and natural degeneration of gill 

 rakers. No specimens examined had the complete 

 complement of rakers fully developed, but they 

 exhibited the possibility of having possessed the 

 full complement of gill rakers at some time; i.e., 

 they had enough rudiments or tubercles or 

 adequate space on the ends of the arch to account 

 for missing rakers. The separation of gill rakers 

 from rudiments is arbitrary, the criterion used 

 here is that a raker so shortened as to be covered 

 with flesh and to have no appreciable flexibility is 

 considered rudimentary. 



Gill-raker degeneration usually begins at the 

 ends of the arch and progresses toward the angle. 

 The outermost rakers first become rudimentary 

 and later become low tubercles. As the rudiments 

 degenerate to tubercles other tubercles form 

 between the gill-raker sites and masses of low 

 tubercles form along the ends of the arch. Quite 

 often tubercles form between fully developed 

 rakers, especially in larger fish. 



Trachinotus sp. — ^Gill rakers were not examined. 



T. carolinus. — Rakers 7 -[-13. Some specimens 

 to about 310 mm. possessed the maximum number 

 (including rudiments) on one limb of the arch. 

 Degeneration is more pronounced on the lower 

 limb, generally progressing with increase in size. 

 Specimens at all sizes above 10 mm. exhibit a 

 complement of 4 to 6 fully developed rakers in the 

 upper arch. On the lower arch, 10- to 30-mm. 

 specimens exhibit a range of 10 to 12 fully devel- 

 oped rakers (the majority have 11); at 50 to 80 

 mm. the range is 9-11 (half the specimens have 

 10); and from 80 mm. on the range is 6-10 (most 

 specimens have 8 or 9). 



T. Jalcatus. — Rakers 8+14. At smaller sizes 

 (10-40 mm.) the gill-raker range is 3-8-1-12-14, 

 with most specimens possessing 5 or more rakers 

 on the upper limb. From 40 to 100 mm. the 

 range is 5-7 -(-10-14 (numbers evenly distributed 

 for upper limb, but with about half the specimens 

 with 12 rakers in the lower limb.) Above 100 

 mm. the range is 3-7 + 8-13 (with more specimens 

 having 5 than any other coimt on the upper limb 

 and with a majority having 11 or 12 on the lower 

 limb). 



T. glaucus. — Rakers 8+14. At 10 to 60 mm. 

 the range is 3-8 + 9-14 (most specimens have 5 or 

 6 on the upper limb and 11 or 12 on the lower 



limb); at 60 mm. and above, it is 4-8+10-11 

 (about half the specimens have 6 on the upper 

 limb and the majority have 10 on the lower limb). 

 There is a tendency toward reduction in the 

 number of fully developed gill rakers with increas- 

 ing size of the fish. 



PREOPERCULAR SPINES 



Very small Trachinotus possess two series of 

 conspicuous preopercular spines (figs. 1, 2, and 3). 

 The series of preopercular-margin spines is located 

 along the edge of the preopercle. Anterior and 

 parallel to this is the series of preopercular-face 

 spines. The margin series consists of three 

 primary margin spines, at and near the angle, the 

 middle (PMS 1) the longest and the upper (PMS 

 2) and lower (PMS 3) being somewhat shorter. 

 These are followed on both limbs by preopercular- 

 margin secondary spines. The secondary spines 

 on the lower limb number two or three and remain 

 fairly constant in number and relative size. The 

 upper secondary spines are few in number at 

 small sizes but increase in number and decrease in 

 size as the fish grows, the result being a finely 

 serrated margin on the upper limb during the 

 latter stages of preopercular-spine development. 

 This is especially true of T. jalcatus. 



The preopercular-face series consists of two or 

 three rather obtuse spines positioned relatively 

 the same as the primary angle spines in the margin 

 series (PFS 1 to 3). These spines, very conspic- 

 uous in small specimens, become relatively smaller 

 with increase in fish size and disappear at about 13 

 mm. The margin series remains conspicuous in 

 fish to the larger sizes. 



At about 13 mm. the preopercle begins to grow 

 laterally, and flat, bony projections begin to 

 radiate between and encroach upon the margin 

 spines. As this encroachment progresses the 

 spines are assimilated into the bony mass with 

 the uppermost and lowermost spines disappearing 

 first. In turn, the bony mass may radiate from 

 the edges of the spines as the spines become a part 

 of the preopercle. In conjimction with this pro- 

 cess, the larger spines, primary and lower limb, 

 become overgrown with flesh prior to bony en- 

 croachment. Any spine so covered is considered 

 assimilated. 



Other bony projections in small Trachinotus 

 are a ridge over and behind the brow and short 



