Nippon Suisan Gakkaishi 59(5), 745-751 (1993) Red and White Muscle Activity of the Jack Mackerel Trachurus japonicus During Swimming Gang Xu,*1,2 Takafumi Arimoto,*1 and Makoto Inoue*1 (Received June 26, 1992) In order to examine the functions of the red and white muscle of jack mackerel Trachurus japonicus during swimming locomotion, the fish was dissected to observe muscle distribution along the body. The electrical activity of the lateral muscle was analyzed using an electrophysiological technique. The ratio of red muscle to total muscle in a transverse section of the fish body reached a maximum at a position between 55% and 65% of fork length from the snout. The red and white muscles accounted for 5.1% and 61% of the body weight respectively. The white muscle was 12 times as heavy as the red muscle. In the electromyographic observations, the red muscle was active in sustained swimming at low speeds, whereas there was no electrical activity from the white muscle at speeds below 108cm/s for fish of 17.8cm in fork length. The bursts of discharge ap pearing in the electromyograph were measured for three components: frequency, amplitude, and duration. The frequency increased in proportion to swimming speed in both muscles. The tendency for the amplitude to increase with swimming speed was much more re markable in the red muscle than in the white muscle. The duration in the red muscle decreased, whereas in the white muscle it rose with the swimming speed. The results indicate that for jack mackerel only the red muscle is used in sustained swimming, while the white muscle is used during burst swimming above a threshold speed of 6.4BL/s, together with red muscle. In most fishes the mytomal Iocomotor mus than in the white muscle.3-6) There are only culature is made up of two main fibre types, a few research works with respect to the functions i.s. red and white muscle fibres.1) The red of the red and white muscles and how fish use them muscle is commonly found as a thin superficial relative to swimming speed.3,7-8) In this report, layer below the skin in some species such as the jack mackerel Trachurus japonicus, an im the sardine and the herring, whereas Scombridae portant commercial species in Japan, was utilized such as the skipjack Katsuwonus pelamis have as a experimental species. The relationship a large amount of deep red muscle.2) The ratio between muscle activity and swimming speed was of red muscle to white muscle has been con examined using electrophysiological techniques. sidered to be one of the factors related to the Muscle distribution along the fish body was ecological and locomotor properties of fish. also investigated in relation to swimming locomo There is general agreement that at low sustained tion. swimming speeds only the red muscle is employed and that the white muscle is active only during Materials and Methods burst of high speed, which cannot be sustained for longer periods.1) Histochemical studies in One group of jack mackerel Trachurusjaponicus dicate that the red and white muscles are different 17.4 to 22.0cm in fork length were caught in from each other with regard to innervation and Tomiura Bay., Chiba Prefecture by angling, biochemical characteristics. Observations with while another group 27.8 to 30.8cm in fork an electromicroscope show that more vasa and length were purchased from a fish farm. The mitochondria ara distributed in the red muscle fish used were held at the Banda Marine Labora- *1 Faculty of Fisheries, Tokyo University of Fisheries, Konan, Minato, Tokyo 108, Japan (•™•@•„,—LŒ³‹M•¶,ˆä•ã•@ŽÀ:“Œ‹ž•…ŽY‘åŠw•…ŽYŠw•”). *2 Present address: Fisheries and Marine Institute of Memorial University of Newfoundland, St. John's, Newfoundland, Canada AIC 5R3 (Œ»•Z•Š:ƒJƒiƒ_ƒjƒ…•[ƒtƒ@ƒ“ƒhƒ‰ƒ“ƒh‹L”O‘åŠw). tory of Tokyo University of Fisheries in a 2•~1•~ of six specimens were calculated using Obatake & 1m tank with circulated water at about 18•Ž for Heya's method. That is, at first the muscle volume a week before the experiments from April to July was calculated by integrating the areas, and then 1989. the specific gravity of 1.05 was multiplied by the In order to investigate the distribution of red volume. One specimen of 21.8cm was immersed and white muscles, ten specimens of 18.5 to 30.8 in hot water at 60•Ž for 5 minutes and then cm were used. Each was cut into eight round skinned so that the myotomes could be observed slices such that the transverse sectional area of from the lateral view. each round slice could be measured. The meas The bipolar electrode shown in Fig. I was made uring procedure was as follows: the specimens of enamel-insulated stainless steel wires (MT were killed by anaesthetizing with solution MS222 Giken) of 10mm in length and 0.2mm in diameter. and then frozen at -15•Ž for 3 hours. The The insulation was removed 1mm from its two specimens which were frozen into a moderate tips, which were separated by 1mm. The in hardness and a straight body shape were cut at sulated copper wires of an XBT probe were used seven points 25, 35, 45, 55, 65, 75, 85% of fork as leads to connect with the ends of the electrode, l ength (L) starting from the snout. All the trans which was cemented with a syrup of perspex in verse sections were recorded using a still camer chloroform and had dimensions of 10mm in (Canon, AE-1; Microlens, 50mm). The areas l ength and 1mm in diameter, weighing 0.5g. of red and white muscles in each transverse Under anaesthesia with MS222 solution (100 section were read by digitizing the photograph ppm), the implantation of electrods was carried using a digitizer (Graphtec, KD4300) and analyzed out. A pair of electrodes were implanted into and calculated by a microcomputer (NEC, the lateral muscle of either the same or of different PC9801). Obatake and Heya9) estimated the weight types. To prevent the electrodes from vibrating of both red and white muscles, based on the as a result of fish body movements, the leads were measurements of muscle area in the transverse sewn and fixed on the base of the second dorsal section along the fish body. The specific gravities fin. of the red and white muscles for the jack mackerel A small flume tank (Fig. 2) was designed to were obtained and found to be similar at 1.05. 9) allow fish to swim stably in its test section of The muscle weight and proportion for a total 70•~ 30•~20 can against the flow at differentFig. 1. Bipolar electrode used for the electromyographic measurements. Fig. 2. Diagram of the electrophysiological apparatus and a small scale flume tank. Fig. 3. Lateral and transverse section views of a fish body, showing the distribution of red and white muscles. velocities up to 185cm/s. This flume tank Results provided a constant flow in the most portions of the test section, except areas within 2.5cm Muscle Distribution of each wall. After the implantation, the fish The muscle distribution could be observed were moved into the flume tank for recovery and clearly as shown in Fig. 3. In lateral views, the then acclimated at 20cm/s for 15 minutes. The superficial red muscle began at a position just electrophysiological apparatus consisted of a posterior to the operculum extending towards 2-channel high sensitivity amplifier (Nippon the tail along the lateral line and ended in the last Koden, AB-632J) with a filter and a 2-channel caudal spine. The myotomes were M-shaped digital storage oscilloscope (Iwatsu, DS-6612C), and locked into each other. The red muscle with a memory card (128KB) for recording and became thinner towards both dorsal and ventral analyzing data. In addition, two video cameras sides where it overlaid the white muscle much (Sony, CCD-V90) were used to simultaneously more thinly than in the vicinity of horizontal record the fish body movements and electro septum. The maximum width of the red muscle myographs from an oscilloscope. occurred at a position of 48%L from the snout. The amplifier was set at a sensitivity range of In the transverse section, most of the red muscle 0.1mv and the filter at a band width of 43 to was observed to be distributed in the superficial 1000Hz. Altogether ten specimens of 17.4 to layer. Some red muscle which was different from 20.7cm, weighing 70 to 122g, were examined. the deep red muscle found in the skipjack pene The flow velocity was set at several levels increas trated a deep layer near the vertebra. The areas ing from an initial level of 47cm/s to a maximum of red and white muscles in each transverse section of 154.3cm/s. Electromyographic recording was were obtained from specimens of 18.5 to 18.6 done at each flow velocity where steady swimming cm (Fig. 4). The maximum area of red muscle was maintained for more than 5 minutes. Here, was found between 55%L and 65%L, whereas the swimming speed of the fish was considered that of white muscle was between 35%L and to be equal to the flow velocity of the flume tank. 45%L. The area of white muscle decreased After each trial, the fish was dissected to determine quickly behind the 55%L position. However, the exact position of the electrode in the muscle. in the vertical direction along the fish body there Table 1.