FLOUNDERS OF THE GENUS PARALICHTHYS AND RELATED GENERA 



IN AMERICAN WATERS 



By Isaac Ginsburg, Fishery Research Biologist 



Tliis report is nn account of tlie iinjioi'taiit trroiip 

 of fliittishes bel(mfiiii<;; to the ^eiuis Paralivhthys, 

 and the closely related genera Hippoglossina and 

 I'se)/dorhoinhuj<. which occur in Aniei'ican watei-s 

 and, in the agfjregate, are food fishes of great eco- 

 nomic importance. Three of the leading species, 

 tlie summer flounder, the southern flounder, and 

 tlie California halibut, add annually nearly 20 

 million pounds to the commercial catch of the 

 United States. Statistics are not available for 

 some other species which are of lesser economic 

 importance or occur on the coasts of Central and 

 South America. The combined catch of all the 

 lesser species is probably considerable at present 

 and will very likely increase with future advances 

 in exploitation of the natural resources of the 

 American continents. In view of the importance 

 of these species, it is remarkable how little we 

 ivuow of their biology. Such knowledge is a pre- 

 i-equisite to the wise exploitation of any species. 

 This report presents some basic knowledge of the 

 species, derived from first-hand, accurately deter- 

 mined data, which is necessary to their further 

 study. 



In order to understand properly the species of 

 Paralk-hthy,^. it is necessary to consider also those 

 that belong to Ilippoglo>iSina and P-'iendo/ho-mhiis, 

 as the species of these three genera form an inter- 

 related, closely knit, and compact group. A seri- 

 ous drawback to a I'ational study of their life his- 

 tories is the difficulty of properly distinguishing 

 the species, which are so closely related that where 

 two or more occur together considerable difficulty 

 lias been encountered in tiying to refer specimens 

 to their respective species. It is true that Jordan 

 and Gilbert (Bull. U. S. Nat. Mus., 16: 8i;-2-823, 

 1883) long ago indicated in broad outline the 

 structural characters by which the connnon species 

 may be distinguished; but in Parulichthys that 

 did not prove sufficient. Descriptions based on a 

 few specimens may be of use in separating matei'ial 

 in btdk, but they are insufficient to identify a 



consi(leral)le percentage of individual fish. The 

 chief characters distinguishing the species are of a 

 meri.stic nature. The extent of intraspecific vai'ia- 

 tions in these characters is considerable. More- 

 over, the species are closely related and they ap- 

 proach one another or even intergrade somewhat 

 in these characters. Consequently, when speci- 

 mens at or near the border line with respect to one 

 or more structural characters are examined, they 

 a))])ear to be inseparable specifically, and doubt is 

 thus cast on the distinctness of the species. 



The difficulties encountei-ed in properly distin- 

 guishing the species concerned may be appre- 

 ciated by a consideration of two treatises dealing 

 with those species. Hildebrand and Cable (Bull. 

 U. S. Bureau of Fisheries 46:464, 1930) state: 

 "■. . . the present writers are unable to separate 

 the representatives of this genus [Parali^tithy^^, 

 occui-ring locally [at Beaufort, N. C], into more 

 than two groups (species?) . . ." The fact is 

 that three common species are present at Beaufort. 

 The data given by these authors on the chief dilfer- 

 entiating characters nearly agree with those de- 

 termined by me. Many of their specimens formed 

 the basis of my studies. Their figures 79-81 rep- 

 resenting the frequency distributions of the num- 

 bers of gill rakeis and anal and dorsal rays evi- 

 dently are bimodal polygons which, taken sepa- 

 rately, would nn(lerstan(lal)ly lead to the state- 

 ment quoted above. However, it is of the utmost 

 importance to correlate the data on wliirh the 

 p<iiygons are based. To illustrate, their iigurc 7'.) 

 consists of two well-defined polyg<jns wiiich 

 tomii at a point, and seemingly it re])resents not 

 moi'e than two s])eties. Howevei', were the fre- 

 (|uency distributions of the number of anal rays 

 of the specimens represented in the left polygon 

 gra]ihed separiitely. the result would be a polygon 

 similar to their figure 80. That is, the left poly- 

 gon represents two s|)ecies, albigutta and letlw- 

 stigiiHi. while the right jiolygon repivsents 

 dciitatwi. Similarly we may use their ligure 80 



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