Notes on Hybrid Sunfishes 



CARL L. HUBBS 



Museum of Zoology, University of Michigan 





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The hybridization of fishes in nature 

 is a subject of interest to aquarists, as 

 well as to systematic ichthyologists and 

 geneticists. It has even been suggested 

 that hybridization plays a part in that 

 complex process known as "the origin of 

 species," but there has been too much 

 suggesting, and too little actual study, in 

 such discussions. Definite knowledge is 

 yet too meager, in the case of fishes at 

 least, to permit of a discussion of the 

 general aspects of natural hybridization. 

 First, we should determine the fre- 

 quency, indeed the very existence, of hy- 

 bridization in nature between fish species. 



David Starr Jordan has stated that al- 

 though thousands of American salmon 

 and trout had passed under his examina- 

 tion, he has never yet seen an individual 

 which he had the slightest reason to re- 

 gard as a "hybrid :" "It is certainly il- 

 logical to conclude that every specimen 

 which does not correspond to our closet- 

 formed definition of its species must 

 therefore be a 'hybrid' with some other. 

 There is no evidence worth mentioning, 

 known to me, of extensive hybridization 

 in a state of nature in any group of 

 fishes. This matter is much in need of 

 further study." Granting the wisdom and 

 critical value of these remarks, it must 

 be observed that they require some modi- 

 fication. In Europe, a number of hy- 

 brids between distinct species, and in 

 some cases between distinct genera, of 

 the carp family (Cyprinidae) , have not 

 only been recorded but also described 

 and studied, and occasionally found not 



rare locally. Trout variously interme- 

 diate between supposed species, and sim- 

 ilar to hybrids produced in the hatcher- 

 ies, have been taken in the streams of 

 both Europe and America. Poeciliod 

 fishes have been obtained in Central 

 America, which resemble hybrids readily 

 produced in aquaria between the genera 

 Platypoecilus and Xiphophorus. To 

 mention but one other case, sunfishes in- 

 termediate between the warmouth bass 

 (Chaenobryttus gulosus) and several 

 species of Lcponiis, occurring in the Po- 

 tomac basin, have lately been interpreted 

 as hybrids (by Radcliffe and by Mc- 

 Atee and Weed). 



Among the hundreds of sunfishes 

 (Centrarchidae) readily referrible to the 

 ten very distinct and abundant species 

 of the region, which the writer has col- 

 lected in waters tributary to Lake Michi- 

 gan and Lake Erie, there were obtained 

 nine individuals which cannot be refer- 

 red to any known species. Six of these 

 were seized in the lagoon of Jackson 

 Park, in the city of Chicago, in which 

 body of water the following species of 

 typical sunfishes (the genus Lepomis), in 

 addition to the warmouth bass {Chaeno- 

 bryttus gitlo'sus), occur and breed (as 

 the present writer has observed in the 

 number of Aquatic Life for July. 1919) ; 

 the blue-gill (L. incisor), the most abun- 

 dant species ; the pumpkin-seed (X. gib- 

 bosus), abundant, but less so than the 

 blue-gill, and the blue-green sunfish (L. 

 cyauellus) , not rare, but probably never 

 abundant. 



