SHORT BIGEYE IN WESTERN NORTH ATLANTIC 



113 



Bermuda also furnishes abundant coral or rock 

 substrate. 



Temperature is possibly the most basic limiting 

 factor in the distribution of P. alius, as the short 

 bigeye is a subtropical or tropical species. Wlicrc- 

 ever conditions of temperature are suitable, 

 however, the bottom type seems to be especially 

 important in the success of permanent populations 

 of adults. 



Specimens are usually taken singlj' or in twos 

 or threes, but it is not known whether this seeming 

 rarity is a real phenomenon or a false impression 

 gained from the secretive habits of the species as 

 juveniles and adults and from the limited collec- 

 tions of pelagic forms. The collection of a large 

 group of prejuveniles (24 specimens, WHOI col- 

 lection, Aug., 19-20 1953, table 1) and an even 

 larger series of adults in a single trawl haul (32 

 specimens, BLBG, Silver Bay station 1393, table 1) 

 suggest the latter premise to be correct. Other 

 museum collections from northern waters (table 1) 

 indicate aggregations also, though in these in- 

 stances data are not specific and complete enough 

 for certainty. 



EFFECT OF HABITAT ON METAMORPHOSIS 



Results of recent studies (Parr, 1930: p. 58; 

 Hubbs, 1941: p. 184, 1958: p. 282; Breder, 1949: 

 p. 296; and M. C. Caldwell, in press) make it ob- 

 vious that a wide variety of marine fishes which as 

 adults occupy a bottom habitat have pelagic lar- 

 vae and prejuveniles which undergo considerable 

 change in appearance in their transition from the 

 pelagic to the bottom habitat. Such stages have 

 frequent!}^ been described as separate species or 

 genera (Hubbs, 1958). Furthermore, it has been 

 shown (Breder, 1949) that the specific size (or age) 

 of the individual does not dictate time of change 

 in form, but rather that the environmental change 

 seems to trigger the metamorphosis after the de- 

 layed development. The fish maintains its pre- 

 juvenile appearance while continuing to grow 

 until, probably within limits, the attainment of 

 suitable conditions of environment. Such an ar- 

 rested development is known for invertebrate 

 marine animals (Thorson, 1957: p. 482) as well as 

 for fishes (Breder, 1949: p. 296; M. C. Caldwell). 

 As a consequence, a prejuvenilc still in its pelagic 

 environment may actually be larger than another 

 of its kind which is in the proper habitat. It is 

 this phenomenon that has resulted in confusion 



leading to the description of the larger or equally 

 sized prejuvenile of a well-known adult as a sepa- 

 rate form. 



Pseudopriacanthus alius exhibits such a change 

 of appearance and shows this differential or de- 

 layed development related to time of settling to 

 the bottom. 



Metamorphic stages in P. altus are quite 

 different, and several fisherman told me that there 

 were possibly two species of Pseudopriacanthus in 

 the western North Atlantic. One was said to be 

 a "dwarf," which was immediateh' suspect. The 

 "dwarf" form proved to be merely the prejuvenile 

 stage of P. altus. With the differential develop- 

 ment in relation to habitat, the "dwarf" form had 

 been seen that was larger than the "normal" form. 

 No large specunens of the "dwarf" form were 

 known simply because they either transformed if 

 the proper habitat was attained or died if it was 

 not. Although a simple method of detecting 

 transitional stages, based on color pattern, was 

 later found, the color pattern would not be par- 

 ticularly noted on casual observation. Hubbs 

 (1958: p. 282) noted that "prejuveniles meta- 

 morphose verj' rapidlj- into the juveniles, which 

 are much more like the adult. For this reason, 

 transitional specimens are seldom encountered." 



Thus, the fishermen had seen either large pre- 

 juveniles or transformed specimens of a similar or 

 greater size — the two having quite different ap- 

 pearances. None of the form with the adult 

 appearance was found smaller than about 50-55 

 mm., which made the validity of the "dwarf" form 

 even more suspect, since this is about the ma.xi- 

 mum size for the latter. Figure 2 illustrates the 

 two forms in question. They look very different, 

 and as the difference in their standard lengths is 

 only 2 mm., the possibility of two species was 

 reasonable, if one had only these specimens. 

 Note the differences in overall bodj- color, spinous- 

 fin membranes, and especially eye size. These 

 two specimens are extremes of a gradient of 

 general appearance. 



It was necessary to find an obvious character, 

 showing the extremes as well as indicating inte- 

 gration, in order to separate the three groups 

 (pretransformed, transforming, and transformed) 

 with relation to size and habitat. The color pat- 

 tern of the caudal and soft parts of the vertical 

 fins proved useful in this respect. The pre- 

 juvenile pattern consists of immaculate or spotted 



