FISHES OF THE GULF OF MAINE 



493 



numerous along the rockbound coasts in the Gulf 

 of Maine. In Scandinavian waters according to 

 Smitt 60 they often take refuge inside large empty 

 mussel shells. But as he remarks, there is no 

 ground for the accusation that rock eels enter 

 live bivalves of any sort to devour them. Whether 

 they seek such places of concealment in deeper 

 waters is not known. 



When disturbed they squirm like eels. Eel- 

 like, they swim by sidewise undulations, and they 

 are so active and so slippery (hence the name 

 "butterfish") that it calls for quick work to catch 

 one by hand, even in a very small puddle. 



Very little is known of the diet of the rock eel, 

 except that it is carnivorous and that various 

 molluscan and crustacean fragments have been 

 found in their stomachs. Vinal Edwards records 

 small amphipods, shrimps, and worms in the few 

 that he examined at Woods Hole, but we have no 

 first-hand information to offer on this point. 

 In turn, rock eels have been found in the stomachs 

 of various larger fishes, especially of cod, in New 

 England waters. 



So far as known the rock eel is resident through- 

 out the year wherever it is found ; at most it may 

 move out from the beach into slightly deeper 

 water in winter to escape chilling. 



Breeding habits. — It is necessary to turn to 

 European sources for information about its breed- 

 ing habits, for its spawning has not been seen in 

 American waters. In the eastern Atlantic and 

 in the North Sea 61 it spawns from between tide 

 marks down to 12 fathoms or more, from Novem- 

 ber to February or March. And its spawning 

 season probably is the same in our Gulf, for eggs 

 apparently belonging to the rock eel have been 

 found off Rhode Island late in December. 62 A 

 female from Peconic Bay, N. Y., contained 686 

 eggs. 63 These, by European accounts, are about 

 2 mm. in diameter, opaque, whitish, but iri- 

 descent on the surface, with a single globule of 

 about 0.6 mm., and they are laid in holes or cran- 

 nies. In British waters the rock eel usually 

 chooses empty oyster shells, or the holes that are 

 made in the limestone rocks by the boring bivalve 



Pholas for the purpose, but there are no oysters 

 in the Gulf of Maine, except in Cape Cod Bay, 

 and the local Pholas is unable to bore into the 

 hard granite rocks of our coast line, so the rock 

 eels must seek other nesting sites. Perhaps large 

 mussel shells may serve them, or any crevice. 

 The eggs are adhesive, and both the parents have 

 been observed rolling them, by coiling around 

 them, into balls or clumps an inch or so across, 

 in which they stick together. 



In European waters incubation occupies from 

 8 to 10 weeks, during which period the parent fish 

 of both sexes have been seen lying close beside the 

 egg clumps. But since Ehrenbaum 64 described 

 the parent as "very negligent" in the aquarium, it 

 seems that they merely seek the nesting holes as 

 convenient shelters, and not that they actually 

 guard the eggs. 



» Scandinavian Fishes, vol. 1, 1892. p. 223. 



11 Macintosh and Masterman (Life Histories of British Marine Food- 

 Fishes, 1897, p. 210) and Ehrenbaum (WissenschaftlicheMeeresuntcrs., Hel- 

 goland, N. Ser., vol. 6, 1904, p. 160) give accounts of its spawning and of its 

 larval development. 



u Tracy, 40th Rept. Comm. Inland Fish., Rhode Island, 1910, p. 151. 



" Nichols and Breder, Zoologica, New York Zool. Soc, vol. 9, 1927, p. 159. 



Figure 258. — Larva (European), 18 mm. After Ehren- 

 baum. 



Figure 259. — Larva (European), 20 mm. After Ehren- 

 baum. 



Rock Eel (Pholis gunnellus). 



The larvae are much larger at hatching (about 

 9 mm.) and further advanced in development 

 than those of most of the fishes that lay buoyant 

 eggs. Older larvae of the rock eel resemble 

 corresponding stages of the launce and of the 

 snake blenny in their extremely slender form. 

 But they are easily distinguishable from both 

 these species by the presence of a row of small 

 black pigment spots below the intestine, instead 

 of above it, and from the herring (the only other 

 very slender larvae apt to be met in any numbers 

 in the Gulf at the same season) by the location of 

 the vent about midway of the body (fig. 259), and 

 by the fact that their tails are rounded, not forked. 

 The 12 black dorsal fin spots so characteristic of 

 the adult are first noticeable against the trans- 

 parent trunk in young fry of 25 to 30 mm. The 



»• Wissenschaftliche Meeresuntersuchungen, Helgoland, N. Ser. vol. 6, 

 1904, p. 161 



