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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



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45 - 



T I I r 



ox 



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10 



50 

 HEAD LENGTH 



Figure 4. — Relation of eye diameter to head length in Psuedopriacanthus alius. (Untransformed larvae and prejuveniles 

 represented by crosses, transforming prejuveniles by open circles, and transformed juveniles and adults by small 

 dots.) 



men than any found in nature (ca. 65 mm. the 

 largest). The fish was found dead on the floor 

 beside the aquarium, which might suggest that 

 some force drove the transitional individual to 

 seek a more suitable habitat, and that its only 

 method of escape was to leap. 



In relation of eye diameter to standard length, 

 there often is a striking difference between the 

 pelagic and bottom forms — the latter having a 

 relatively larger eye at comparable sizes. Also, 

 regression lines estimated visually show that the 

 increase in eye diameter per unit of increase both 

 in length of fish (fig. 3) and in length of head 

 (fig. 4) is greater in the smaller (pelagic) fishes 

 than it is in the larger (bottom) forms. Rather 

 than there being an inflection in the zone of 

 transformation (about 35 to 65 mm.), there 

 appears to be a step, the result of a very rapid 

 and apparently sudden increase in relative (as 

 well as actual) eye size during transformation. 

 The fish assume the bottom habitat at different 

 sizes, and it is in the size range of the transforma- 

 tion that /'. alius changes from a pelagic to a 

 bottom habitat. Once the relative size of the 

 eye reaches its maximum — in the size range 

 (35-65 mm. standard length) at which the bottom 



habitat is assumed — it maintains a constant rate 

 of increase (but lower than initially) to the 

 largest size, though the eye diameter may be 

 relatively smaller in larger fish than in the pelagic 

 young.' 



Figure 5 demonstrates the relation of eye 

 size to habitat, length of the fish, and stage of 

 development suggested by fin coloration. The 

 open circles represent specimens dip-netted, sur- 

 face-netted, or washed ashore. The solid squares 

 represent specimens either demonstrated or sug- 

 gested to have come from a bottom habitat. 

 A few nontransformed specimens taken from a 

 bottom habitat are indicated by open squares. 

 Transitional stages from each habitat, as de- 

 termined on fin color pattern, are represented 

 by hall-solid symbols. The dashed line suggests 

 the dividing line between pelagic and bottom- 

 dwelling specimens, with a few exceptions among 

 bottom forms. 



It is evident that pelagic individuals not 

 finding suitable habitat continued to grow and 

 mav exceed in length the bottom-dwelling in- 



' Some of the smallest larvae (fig. 6) have a much smaller eye in relation 

 to standard length than most of the adults, but as they differ so from the 

 adults in many features they are omitted from this discussion. 



