190 THE ZOOLOGIST. 



OBSERVATIONS UPON THE BEHAVIOUR OF A 

 CAPTIVE ROCKLING. 



By H. N. Milligan, F.Z.S. 



The Five-bearded Rockling (Motella mustela) which is the 

 subject of this article was obtained by me at Walton-on-the-Naze 

 on December 3rd. I did not watch the movements of the fish 

 with any particular care during the first week or ten days of its 

 residence in an aquarium at the Horniman Museum, and the 

 following remarks must therefore be understood to refer to the 

 time subsequent to the first ten days of its captivity. 



A plan of the aquarium in which I placed the Rockling is 

 given in the accompanying figure, the back and two sides of the 

 tank being of dark blue slate and the front of glass. The fish 

 made its resting-place beneath and behind the shelving rock 

 lettered A, which stands nearly in the middle of the floor of the 

 aquarium, in the position shown in dotted outline B. Except 

 when tempted to follow pieces of raw beef (which it will seize 

 and swallow very readily) held close before its snout in wooden 

 feeding-forceps, the Rockling did not seem to care to leave this 

 place in the daytime, and I have only twice seen it do so 

 voluntarily. In the night, however, it wanders freely. I have 

 visited its tank after dark with an electric hand-lamp, whose 

 light I could turn on and off at will, and have observed that the 

 fish searches and researches every part of the aquarium, and 

 that its movements have a vigorous and determined character 

 not displayed in the daytime. I often find in the morning that 

 the pebbles on the bottom of the aquarium have been disturbed 

 in a way which shows that the fish has ploughed through and 

 through them with its heavy body during the night. The 

 average size of the pebbles is about that of a hazel-nut, so 

 that the Rockling must use considerable force in shifting masses 

 of them. 



The fish almost invariably lay in its resting-place B with 

 its tail directed towards the left side of the tank. During its 

 first twenty-one weeks in the tank, I can only remember four 



