NOTES 



EFFECT OF SWIMMING SPEED ON THE 



EXCESS TEMPERATURES AND ACTIVITIES 



OF HEART AND RED AND W HITE MUSCLES IN 



THE MACKEREL, SCOMBER JAPOSICUS 



Body temperatures of most fish t^-pically are about 

 the same as the water in which they swim for 

 much of the heat generated by muscular activity is 

 ducted away via the circulating blood and lost b\' 

 convection at the gills and body surface. 



Some scombrids and lamnid sharks consei'\'e 

 muscle heat using countercurrent vascular heat 

 exchangers tretia mirabiliai so that temperatures 

 are maintained significantly above ambient in the 

 brain, eyes, red and white swimming muscles, and 

 viscera (Carey et al. 1971; Stevens and Frj' 1971; 

 Linthicum and Carey 1972; Graham 1973). In 

 other fishes lacking these heat conserving devices, 

 only small temperature excesses above ambient 

 have been recorded, but rarely more than VC 

 (Stevens and Fry 1974). Since heat production 

 must depend primarilj' on work output by the 

 locomotor musculature, we have examined effects 

 of swimming speed on the magnitude of the small 

 temperature excesses in a "cool" scombrid not 

 equipped with the retia exchangers, the mackerel. 

 Scomber Japojjicus (locally the Pacific mackerel = 

 chub mackerel). 



Another important question concerning scom- 

 brid locomotion is how contractions of red and 

 white muscle fibers are staged as swimming speed 

 increases. It is generally thought that red muscle 

 provides power for cruise swimming and that 

 white muscle functions in "burst" swimming 

 (Rayner and Keenan 1967). Red muscle is pre- 

 dominately aerobic and utilizes fatty acids as the 

 major energy source whereas white muscle (which 

 uses glycogen) usually functions anerobically 

 (Gordon 1968; Bilinski 1974). The second objective 

 of our study was to determine how heart rate and 

 red and white muscle activity of S.japonicus are 

 affected by swimming speed. For this purpose, 

 electrodes were implanted into the pericardial 

 space and in swimming muscles of fish so that 

 simultaneous records of electrocardiograms 

 (ECG's) and red and white electromyographs 

 (EMG's) could be obtained. 



The genus Scomber is a primitive member of the 

 familv Scombridae (Kishinouve 1923). It has a 



fusiform shape, is less heavilj' bodied than the 

 skipjack tuna. Katsuwonus pelamis. and other 

 tunas, but shares several characteristics with 

 warm-bodied species; they swim continuously 

 (swim bladders are reduced or absent), have high 

 rates of oxygen consimiption (Baldwin 1923: Hall 

 1930). and have high blood hemoglobin levels 

 (Greer-Walker and Pull 1975 1. They are also ob- 

 ligatorily dependent upon ram gill ventilation as 

 adults (Roberts 1975) and have large gill siirface 

 areas with a high diffusion efficiency (Hughes 

 1966; Steen and Berg 1966). 



Materials and Methods 

 Surgical Procedures and Swimming Experiments 



The general procedure was to implant either 

 thermocouples or cardiac (ECG) and muscle 

 (EMG) electrodes into mackerel which were then 

 placed in a Blazka-Fry tunnel respirometer ( 12 cm 

 i.d.) to swim at controlled velocities. Fifteen 

 specimens (35-40 cm fork length (FL); 0.38-0.62 

 kg) were obtained from regularly replenished and 

 maintained mackerel stocks at the Southwest 

 Fisheries Center La Jolla Laboratory. National 

 Maiine Fisheries Service. NOAA. After netting, 

 each fish was anesthetized in a large basin of 

 oxygenated seawater containing 0.2 g 1 of tricaine 

 methanesulfonate (Crescent Research Chemical, 

 Inc.)^ and placed on an operating table where its 

 gills were perfused continuousl.v with a fast flow of 

 oxygenated seawater containing a small amount 

 of the same anesthetic (0.08 gl). Thermocouples 

 (0.127 mm in diameter copper constantan, 

 polyvin3i chloride insulation) or electrode pairs 

 (hooked. 0.07 mm in diameter stainless-steel, 

 epoxy insulated) were implanted within the 

 pericardial cavity just posterior to the ventricle, 

 and in red and white muscles just under the lead- 

 ing edge of the second dorsal fin. 



The white muscle thermocouple tip was placed 

 midway between the vertebral column and the 

 lateral edge of the body at the level of the horizon- 

 tal midline. Preliminary dissections confirmed 

 that red muscle in S. japonicus occurs in bands 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Ser\ice. NOAA. 



FISHERY BULLETIN; VOL. 76. NO. 4. 1979. 



861 



