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The strengthening of cod connective tissue during starvation
Camp. Biockem. Pkyriol., 1972, Vol, 4lA, pp. 39 to 42. Pergamon Press. Printed in Great Britain
THE STRENGTHENING OF COD CONNECTIVE TISSUE DURING STARVATION J. LAVETY
and R. M. LOVE
Torry Research Station, Aberdeen, Scotland (Received
4 June 1971)
Abstract-l. During starvation, protein is removed from cod musculature and the water content increases, giving rise to a much softer and weaker tissue. 2. The myocommata, which bind the muscle blocks together, simultaneously become much stronger. 3. This may be a mechanism to prevent the break-up of the fish during depletion, and may explain differences in the properties of myocommata from cod caught on different fishing grounds.
INTRODUCTION BLOCKS of parallel contractile muscle cells in the musculature of fish are separated from each other by sheets of connective tissue known as myocommata. Collagenous threads leave each myocomma approximately at right angles, weaving between the muscle cells, probably surrounding them and eventually joining up with the next myocomma. In this way the cells are bound to each other and to the myocommata, which appear to transmit the force from muscular contraction to the vertebral column (Love, 1970). In May and June 1966 the physical properties of myocommata dissected from cod (G&S morhua L.) caught on different fishing grounds between Scotland and W. Greenland were compared (present writers, unpublished). No obvious differences appeared until fish from the Faroe Bank were examined. The cod caught here were filleted immediately after being caught, while the muscle was still twitching, but although there had been no time for the collagen to be damaged, e.g. by warming to air temperature, it was found impossible to dissect out the myocommata, which were very soft and gelatinous instead of being smooth, firm membranes. All the fish caught on that occasion on Faroe Bank exhibited the phenomenon, but we have not seen it since-Faroe Bank cod caught at the same time the following year had normal tough myocommata. The observations described here appear to shed light on the phenomenon. THE
MATERIALS
AND METHODS
Cod (Gadus morhua L.) caught at various times in the vicinity of Aberdeen were kept for various periods without food in an aquarium at 9°C. They were killed by a blow on the head, quickly gutted and then filleted in a 0°C room where the dissection was also carried out. 39
40
J. LAVBTY AND K. M. LOVE
Myocommata from the anterior third of the fillet were dissected from the strip of musculature immediately dorsal to the lateral line. Starting on the cut surface of the fillet, one face of a myocomma was exposed and then freed from muscle celis with a “shaving” action, using light, broad strokes with a Swann-Morton No. 24 scalpel. Parallel cuts were then made, 1 cm apart, from top to bottom, and the resulting myocomma strip was severed and freed from muscle on the reverse side in the same way. The strip was tied at each end with linen thread to the apparatus illustrated in Fig. 1, the tissue between the two ties measuring 1.5 cm. The strip was maintained at 0°C in a O-05 M phosphate buffer of pH 7.0 and pulled until it broke, the maximum tension generated being shown by the pen recorder.
FIG. 1. Apparatus for measuring the breaking strain of a strip of myocomma 1 cm wide. The strip, indicated by the arrow, is attached with thread to the buffer chamber below and the beam a above. The beam pivots freely at its centre, and when the threaded bar b is slowly rotated by the motor at the top, the tension rises, being measured by the transducer c, the output of which is connected to a pen recorder.
The water content of the tissue was determined by dissecting about 10 g of whole musculature from the anterior part of the fillet, placing in a tared basin, chopping into about twenty pieces with scissors and maintaining in an oven at 100°C for 7 days, when the weight loss was taken as the water content. In the case of severely starved fish this sample had to be removed immediately after filleting, because fluid, probably extracellular in origin (Love et al., 1968), flowed freely from the cut surface almost immediately. RESULTS
It was shown by Love (1960) that the water content of the musculature gives a general guide to the overall nutritional status of the fish, the value for non-starving cod being near 80 per cent and depletion being shown in a content of 81 per cent or more. In the present work the breaking strain of the myocommata has been plotted against the water content, and hence against the nutritional status. As the thickness of the myocommata depends on the size of the fish (Love, 1970) and because the fish used in the present experiments unavoidably varied in size, the results have been subdivided into three groups within which there is little
STRENGTHENING
OF COD CONNECTIVE TISSUR DURING STARVATION
41
variation in body length. Both severely starved and non-starved fish are found within each size-group, so that body length can be discounted in considering the results, which show a striking correlation between the breaking strain and the degree of starvation (Fig. 2). The significant point is that the myocommata become stronger as the fish are depleted, not weaker as might have been expected. The
I 80I
I
I
95
90 Muscle Hz0 %
I
93
FIG. 2. Weight (g) necessary to break myocomma strips 1 cm wide, mounted in the apparatus illustrated in Fig. 1, from cod of varying degrees of depletion as measured by the water content of the muscle (an increase in water indicates an increase in depletion). Each point is the average of 6-10 myocommata. Body lengths: 0, 60-69.9 cm; n , 70-79.9 cm; Cl, 80-89.9 cm.
regression line has been drawn through all the points as though the size differences did not exist-if all the fish had been of the same size the correlation coefficient would have exceeded the present value of +0*828. We aimed to take ten myocommata from each fish and average the results, but most of the musculature was required for other experiments, and in practice, especially among the smaller fish, it was not always possible to achieve this number of samples. The sample size has also been ignored in drawing the regression line. DISCUSSION
Since starvation causes strengthening and probably thickening of the myocommata, it follows that when the myocommata of cod taken from different grounds or at different seasons are compared, their strengths will vary according to the nutritional status prevailing among the fish. It also follows that at some point after the period of natural depletion in the spawning cycle, the myocommata
J. LAVBTY AND R. M. LOVE
42
must weaken again to bring them back to their normal (non-starving) values. It is not unreasonable to suppose that the cod caught in June 1966 on Faroe Bank had reached this “weakening” stage, making their myocommata impossible to dissect. It has already been noticed that the bodies of Pacific herring (clupea pall&i) contain more collagen at the spawning time (McBride et al., 1959a, b) and that this fish ceases to feed during gonad development (McBride et al., 1960), so that some of the sex products must have come from the breakdown of body tissue. These authors suggested that amino acid mobilization for gonad development was probably selective, so that some of the “unused” amino acids could perhaps be utilised for collagen synthesis. Hughes (1963) s h owed that the skin of the Atlantic herring (CZupea Zzarengus) also thickened during the spawning season, and that it thickened further later in the season when the fish ceased to feed. Much work clearly remains to be done in this field, but these results have been reported now to draw attention for the first time to the phenomenon in myoOur histological studies appear to show that the collagen threads commata. between the cells increase in thickness as well, obviously helping to prevent the disintegration of the starving fish, from which much of the muscle cytoplasm has disappeared (Love et al., 1968). Acknowledgements-The work described in this paper formed part of the programme the Department of Trade and Industry. The apparatus (Fig. 1) was a development from an original idea by Mr. V. Mohr.
of
REFERENCES Collagen and HUGHES R. B. (1963) Chemical studies on the herring (Clupea harengus)-VII. cohesiveness in heat-processed herring, and observations on a seasonal variation in collagen content. J. Sci. Fd Agric. 14, 432-441. LOVE R. M. (1960) Water content of cod (Gudus calluvius L.) muscle. Nature, Land. 185, 692. LOVE R. M. (1970) The Chemical Biology of Fishes. Academic Press, New York. LOVE R. M., ROBERTSON I. & STRACHAN I. (1968) Studies on the North Sea cod-VI. Effects of starvation. 4. Sodium and Potassium. r. Sci. Fd Agric. 19, 415-422. MCBRIDE J. R., MACLEOD R. A. & IDLER D. R. (1959a) Identity of the gel factor in herring solubles and means of overcoming its effect. J. ugric. Fd Chem. 7, 646-650. MCBRIDE J. R., MACLEOD R. A. & IDLER D. R. (1959b) Proximate analysis of Pacific herring (CZupeu pallusii) and an evaluation of Tester’s “fat factor”. r. Fish. Res. Bd Can. 16,
679-684. MCBRIDE J. R., MACLEOD R. A. & IDLER D. R. (1960) Seasonal variation content of Pacific herring tissues. r. Fish. Res. Bd Can. 17, 913-918.
Key fishing
Word Index-Cod; grounds;
starvation;
connective tissue ; collagen ; myocomma spawning cycle; Gudus morhuu.
in the collagen
; seasonal
variation
;
THE STRENGTHENING OF COD CONNECTIVE TISSUE DURING STARVATION J. LAVETY
and R. M. LOVE
Torry Research Station, Aberdeen, Scotland (Received
4 June 1971)
Abstract-l. During starvation, protein is removed from cod musculature and the water content increases, giving rise to a much softer and weaker tissue. 2. The myocommata, which bind the muscle blocks together, simultaneously become much stronger. 3. This may be a mechanism to prevent the break-up of the fish during depletion, and may explain differences in the properties of myocommata from cod caught on different fishing grounds.
INTRODUCTION BLOCKS of parallel contractile muscle cells in the musculature of fish are separated from each other by sheets of connective tissue known as myocommata. Collagenous threads leave each myocomma approximately at right angles, weaving between the muscle cells, probably surrounding them and eventually joining up with the next myocomma. In this way the cells are bound to each other and to the myocommata, which appear to transmit the force from muscular contraction to the vertebral column (Love, 1970). In May and June 1966 the physical properties of myocommata dissected from cod (G&S morhua L.) caught on different fishing grounds between Scotland and W. Greenland were compared (present writers, unpublished). No obvious differences appeared until fish from the Faroe Bank were examined. The cod caught here were filleted immediately after being caught, while the muscle was still twitching, but although there had been no time for the collagen to be damaged, e.g. by warming to air temperature, it was found impossible to dissect out the myocommata, which were very soft and gelatinous instead of being smooth, firm membranes. All the fish caught on that occasion on Faroe Bank exhibited the phenomenon, but we have not seen it since-Faroe Bank cod caught at the same time the following year had normal tough myocommata. The observations described here appear to shed light on the phenomenon. THE
MATERIALS
AND METHODS
Cod (Gadus morhua L.) caught at various times in the vicinity of Aberdeen were kept for various periods without food in an aquarium at 9°C. They were killed by a blow on the head, quickly gutted and then filleted in a 0°C room where the dissection was also carried out. 39
40
J. LAVBTY AND K. M. LOVE
Myocommata from the anterior third of the fillet were dissected from the strip of musculature immediately dorsal to the lateral line. Starting on the cut surface of the fillet, one face of a myocomma was exposed and then freed from muscle celis with a “shaving” action, using light, broad strokes with a Swann-Morton No. 24 scalpel. Parallel cuts were then made, 1 cm apart, from top to bottom, and the resulting myocomma strip was severed and freed from muscle on the reverse side in the same way. The strip was tied at each end with linen thread to the apparatus illustrated in Fig. 1, the tissue between the two ties measuring 1.5 cm. The strip was maintained at 0°C in a O-05 M phosphate buffer of pH 7.0 and pulled until it broke, the maximum tension generated being shown by the pen recorder.
FIG. 1. Apparatus for measuring the breaking strain of a strip of myocomma 1 cm wide. The strip, indicated by the arrow, is attached with thread to the buffer chamber below and the beam a above. The beam pivots freely at its centre, and when the threaded bar b is slowly rotated by the motor at the top, the tension rises, being measured by the transducer c, the output of which is connected to a pen recorder.
The water content of the tissue was determined by dissecting about 10 g of whole musculature from the anterior part of the fillet, placing in a tared basin, chopping into about twenty pieces with scissors and maintaining in an oven at 100°C for 7 days, when the weight loss was taken as the water content. In the case of severely starved fish this sample had to be removed immediately after filleting, because fluid, probably extracellular in origin (Love et al., 1968), flowed freely from the cut surface almost immediately. RESULTS
It was shown by Love (1960) that the water content of the musculature gives a general guide to the overall nutritional status of the fish, the value for non-starving cod being near 80 per cent and depletion being shown in a content of 81 per cent or more. In the present work the breaking strain of the myocommata has been plotted against the water content, and hence against the nutritional status. As the thickness of the myocommata depends on the size of the fish (Love, 1970) and because the fish used in the present experiments unavoidably varied in size, the results have been subdivided into three groups within which there is little
STRENGTHENING
OF COD CONNECTIVE TISSUR DURING STARVATION
41
variation in body length. Both severely starved and non-starved fish are found within each size-group, so that body length can be discounted in considering the results, which show a striking correlation between the breaking strain and the degree of starvation (Fig. 2). The significant point is that the myocommata become stronger as the fish are depleted, not weaker as might have been expected. The
I 80I
I
I
95
90 Muscle Hz0 %
I
93
FIG. 2. Weight (g) necessary to break myocomma strips 1 cm wide, mounted in the apparatus illustrated in Fig. 1, from cod of varying degrees of depletion as measured by the water content of the muscle (an increase in water indicates an increase in depletion). Each point is the average of 6-10 myocommata. Body lengths: 0, 60-69.9 cm; n , 70-79.9 cm; Cl, 80-89.9 cm.
regression line has been drawn through all the points as though the size differences did not exist-if all the fish had been of the same size the correlation coefficient would have exceeded the present value of +0*828. We aimed to take ten myocommata from each fish and average the results, but most of the musculature was required for other experiments, and in practice, especially among the smaller fish, it was not always possible to achieve this number of samples. The sample size has also been ignored in drawing the regression line. DISCUSSION
Since starvation causes strengthening and probably thickening of the myocommata, it follows that when the myocommata of cod taken from different grounds or at different seasons are compared, their strengths will vary according to the nutritional status prevailing among the fish. It also follows that at some point after the period of natural depletion in the spawning cycle, the myocommata
J. LAVBTY AND R. M. LOVE
42
must weaken again to bring them back to their normal (non-starving) values. It is not unreasonable to suppose that the cod caught in June 1966 on Faroe Bank had reached this “weakening” stage, making their myocommata impossible to dissect. It has already been noticed that the bodies of Pacific herring (clupea pall&i) contain more collagen at the spawning time (McBride et al., 1959a, b) and that this fish ceases to feed during gonad development (McBride et al., 1960), so that some of the sex products must have come from the breakdown of body tissue. These authors suggested that amino acid mobilization for gonad development was probably selective, so that some of the “unused” amino acids could perhaps be utilised for collagen synthesis. Hughes (1963) s h owed that the skin of the Atlantic herring (CZupea Zzarengus) also thickened during the spawning season, and that it thickened further later in the season when the fish ceased to feed. Much work clearly remains to be done in this field, but these results have been reported now to draw attention for the first time to the phenomenon in myoOur histological studies appear to show that the collagen threads commata. between the cells increase in thickness as well, obviously helping to prevent the disintegration of the starving fish, from which much of the muscle cytoplasm has disappeared (Love et al., 1968). Acknowledgements-The work described in this paper formed part of the programme the Department of Trade and Industry. The apparatus (Fig. 1) was a development from an original idea by Mr. V. Mohr.
of
REFERENCES Collagen and HUGHES R. B. (1963) Chemical studies on the herring (Clupea harengus)-VII. cohesiveness in heat-processed herring, and observations on a seasonal variation in collagen content. J. Sci. Fd Agric. 14, 432-441. LOVE R. M. (1960) Water content of cod (Gudus calluvius L.) muscle. Nature, Land. 185, 692. LOVE R. M. (1970) The Chemical Biology of Fishes. Academic Press, New York. LOVE R. M., ROBERTSON I. & STRACHAN I. (1968) Studies on the North Sea cod-VI. Effects of starvation. 4. Sodium and Potassium. r. Sci. Fd Agric. 19, 415-422. MCBRIDE J. R., MACLEOD R. A. & IDLER D. R. (1959a) Identity of the gel factor in herring solubles and means of overcoming its effect. J. ugric. Fd Chem. 7, 646-650. MCBRIDE J. R., MACLEOD R. A. & IDLER D. R. (1959b) Proximate analysis of Pacific herring (CZupeu pallusii) and an evaluation of Tester’s “fat factor”. r. Fish. Res. Bd Can. 16,
679-684. MCBRIDE J. R., MACLEOD R. A. & IDLER D. R. (1960) Seasonal variation content of Pacific herring tissues. r. Fish. Res. Bd Can. 17, 913-918.
Key fishing
Word Index-Cod; grounds;
starvation;
connective tissue ; collagen ; myocomma spawning cycle; Gudus morhuu.
in the collagen
; seasonal
variation
;