HiRAiwA, Y. K., AND M. Sato. 



1939. On the effect of parasitic Isopoda on a prawn, 

 Penaeopsis akayebi Rathbun, with a consideration of the 

 effect of parasitization on the higher Crustacea in gener- 

 al. J. Sci. Hiroshima Univ., Ser. B, Div. 1, 7:105-124. 



Thielemann, M. 



1910. Beitrage zur kenntnis der Isopodenfauna Ostasiens. 

 Beitr. Naturgesch. Ostasiens. Ahb. Math-Phys. Kl. K. 

 Bayer. Akad. Wiss. II. Suppl.-Bd. 3 Abh., 109 p. 

 TURNER, C. L. 



1924. Studies on the secondary sexual characters of 

 crayfishes. I. Male secondary sexual characters in females 

 of Camharus propinquus. Biol. Bull. (Woods Hole) 

 46:263-276. 



1929. Studies on the secondary sexual characters of 

 crayfishes, IX. Females of Cambarus with aberrant 

 female characters. Biol. Bull. (Woods Hole) 56:1-7. 



1935. The aberrant secondary sex characters of the 

 crayfishes of the genus Cambarus. Am. Midi. Nat. 

 16:863-882. 

 ZONGKER, J. 



1961. Monoecious tendencies in a population o{ Cambarus 

 montanus acuminatus Faxon. M.A. Thesis, Univ. Vir- 

 ginia. Charlottesville, 30 p. 



ISABEL PEREZ FARFANTE 



Northeast Fisheries Center Systematics Laboratory 

 National Marine Fisheries Service, NOAA 

 National Museum of Natural History 

 Washington. DC 20560 



ON THE ROLE OF THE DIFFERENT FIBRE TYPES 



IN FISH MYOTOMES AT INTERMEDIATE 



SWIMMING SPEEDS 



In most fishes the myotomal locomotor muscula- 

 ture is made up of two main fibre types: a super- 

 ficial layer of red fibres overlies the white fibres 

 which form the main mass of the myotome. A 

 spectrum of such differences as mitochondrial con- 

 tent, enzyme activities, blood supply, and innerva- 

 tion (as well as color) distinguishes these two fibre 

 types. The electrophysiogical properties of the two 

 fibre types have only been investigated in a few 

 species, but in all of these the white fibres have 

 been found to propagate muscle action potential, 

 whereas only local nonpropagated activity is seen 

 from red fibres (which are invariably multiply in- 

 nervated). In many (but not all) fishes, there are 

 also other less abundant fibre types in the 

 myotomes, in some respects intermediate between 

 the red and the white fibres (e.g., Patterson et al. 

 1975). 



There is general agreement that at low sus- 

 tained swimming speeds only the red fibres are 

 employed and that the white fibres are active dur- 



ing short bursts of maximum speed, which cannot 

 be long sustained. However, agreement has not 

 yet been reached about which fibres are active 

 during sustained swimming at speeds above the 

 minimum cruising speed. Indirect evidence from a 

 number of teleost species (e.g., Greer Walker and 

 Pull 1973) indicated that the white fibres are ac- 

 tive at these intermediate swimming speeds, as 

 did the direct electromyographic investigations of 

 Hudson (1973). More recently, several workers 

 have suggested that fibres of intermediate type 

 are recruited as swimming speed rises from the 

 minimal cruising speed, before white fibres are 

 activated and the fish attains its maximal 

 sustained speed. In this note, we report elec- 

 tromyographic observations on various teleosts 

 swimming at controlled speeds in a tunnel res- 

 pirometer, which show that the activity of the 

 myotomal fibre types during sustained swimming 

 is different in different fishes. 



Material and Methods 



We studied herring, carp, and trout. Juvenile 

 Pacific herring, Clupea harengus pallasi Valen- 

 ciennes, 15-17.5 cm FL (fork length) were caught 

 by seining in the Georgia Straits, B.C., and held in 

 circulating seawater at the Department of Zool- 

 ogy, University of British Columbia, until swum 

 in a tunnel respirometer (Brett 1964). Herring are 

 delicate fish and did not settle quietly in the res- 

 pirometer at flow lengths below 2-3 body lengths 

 per second (BL/s). Instead, they darted upstream, 

 and fell back again in an irregular manner, so that 

 it was necessary to force them to swim at such 

 speeds from their first entry to the apparatus, 

 without the acclimation period usual when work- 

 ing with other fishes. 



Varnished copper wire ( 40 standard wire gauge) 

 electrodes bared at the tips were placed in the 

 postanal myotomes. The fish were anaesthetized 

 with MS-2221 (Sandoz) and the electrodes sutured 

 to the dorsal surface before being led downward 

 and backward to enter the myotomes. After recov- 

 ery for 30 min or so in a bucket of seawater, the fish 

 were introduced to the respirometer and muscle 

 potentials recorded on a Gould Brush 220 pen re- 

 corder via Tektronix 122 preamplifiers. It proved 

 difficult to record from electrodes whose tips lay 

 amongst the white muscle fibres, but activity from 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



691 



