300 MARKETABLE BRITISH MARINE FISHES 



The Rocklings {MotcIIa tricirrata, ciiiibria, vinstela). 



Disti}ignishi)ig Characters. — The barbels, and the narrow 

 anterior fin sunk in a groove in the back, are sufficient to dis- 

 tinguish these fishes. In the three-bearded species the barbels 

 are long, one at the chin, one on each side of the snout in front of 

 the nostrils : in the four-bearded there is one also on the upper lip, 

 in front of the other pair, while in the five-bearded there is one 

 pair on the anterior nostrils and a pair on the upper lip. The 

 three-bearded kind is chestnut on the back, lighter beneath, 

 and covered with scattered black spots : it grows to 20 inches in 

 length. The four-bearded kind has no spots, and has not been 

 found above 14 inches in length. The five-bearded kind is also 

 without spots, and reaches 18 inches. 



Habitat. — The three-bearded kind is common in the 

 Mediterranean and extends to Norway, the five-bearded kind 

 ranges from Portugal to Iceland, and the four-bearded from the 

 British Isles to the Arctic Ocean. 



Food. — They feed on crustaceans and small fish, and hunt 

 only at night, remaining concealed in holes or under stones in 

 the daytime. The anterior dorsal fin is very narrow, and is 

 frequently kept in a state of rapid vibration in the living fish : 

 the meaning or use of this curious movement is not known. 



The buoyant eggs of the five-bearded rockling were studied 

 by George Brook in his private aquarium in 1884. They measure 

 7 mm. in diameter (not quite -^^-^j inch). They have a simple 

 yolk and a single oil globule, although when first shed there are 

 often three or four oil globules which soon afterwards run 

 together into one. 



The larvae hatched out 5^ to 6 days after fertilisation, at 

 temperatures from 55° to 62°. They were only 2'25 mm. long 

 (t¥Tt inch). The oil-globule is at the hinder end of the yolk-sac ; 

 the fin-membrane is unusually narrow. The black pigment forms 

 two bands or patches on the tail, as in the larva of the hake. 



The later stages of the rocklings are very abundant at the 

 surface of the sea, in summer, but it is difficult to distinguish 

 the different species when very young, in fact until the barbels 

 appear. They are most abundant in May and June, and form 

 largely the food of the mackerel at that season. They have been 



