Anexo Nº 1 Matriz de consistencia

smaller N.neglecta In large cod there is a decrease in fibre cross-sectional areas with increasing size fish

(Greer-Walker,1970 ) . The decrease in fibre size in older cod is explained as a mechanical constraint caused by movement at speed through the water column. Such constraints do not seem to come into play for the labriform swimming N .neglecta, possibly because it does not use such fast swimming speeds as the c o d .

Muscle fibres are generally surrounded by capillaries in proportion to their aerobic metabolic properties

(Romanul,1965 ; Gray & R e n ki n ,1978 ), and their oxygen

requirement (Krogh,1919; Wei b el ,1979). In fish, slow muscle fibres are usually found at densities of about 1:1 with

capillaries, if not higher (Mosse,1979). With such large fibres it might be expected that the capillary density of the muscle would have to be high in order to supply sufficient oxygen to the central portions of the fibres. In N .neglecta there is no correlation between either fish standard length or wet weight and capillary density, although the line of best fit has a slightly negative slope. Hoppeler et al (1981b) have shown a negative correlation between capillary density and size, in a large weight range of African mammals. Fibre cross-sectional area or number is not a

good indicator of the oxygen requirement of the muscle since it is not the fibres themselves, but the mitochondria which are the actual utilisers of the oxygen supplied. The

mitochondrial complement of muscle fibres has been correlated with maximum aerobic capacity (Hoppeler et al,1973; Bylund et al,1977).

If the capillary density is matched with the mitochondrial volume density there is a good agreement in mammals (Hoppeler et al,1981a) and for fish species although the Antarctic

species and the conger eel appear not to fit this trend (Fig. 4.5). N .neglecta and C .aceratus therefore have low capillary densities when compared with species of similar mitochondrial

volume density. However, the capillary surface and volume densities for the Antarctic species (Table 4.1) are comparable with temperate fish species which have higher haematocrits and haemoglobin concentrations (Egginton & Johnston,1982a). This means that despite the lower capillary density, the volume of blood in the capillary bed, and the surface area of

capillaries available for gas/metabolite exchange are similar in Antarctic and temperate fish. This is brought about in the Antarctic species through the existence of large bore

capillaries (Fitch & Johnston,1983 ; Fitch et al,1984), which are much greater in cross-sectional area than in temperate fish of similar size (Table 4.1). So the capillary density appears not be a good descriptor of the exchange properties of the vascular bed, at least in Antarctic species.

Quantification of surface and volume densities of the

capillaries might be a better indicator of the vascular bed (Egginton & Johnston,1982a). It must also be remembered that

capillary density does not relate exclusively to aerobic metabolism; capillarisation of the white fibres is

relatively too abundant when comparing oxidative capacities with red muscle (Gray & Renkin,1978). The involvement of capillaries with substrate supply, lactate removal and heat removal must all be accounted for (Hoppeler et al,1981).

If the mitochondrial volume density is plotted against size (Fig. 4.4) there is a negative correlation (r= -0.863; P<0.01). The same situation occurs in mammals although with a large variability (Mathieu et al,1981), and quantitative histochemical observations seem to support a decrease in the mitochondrial content of fibres with increasing muscle fibre cross-sectional area (Gauthier & Padykula,1966). The

situation is further complicated by the presence of two mitochondrial populations; subsarcolemmal mitochondria (SS)

found at the periphery of the fibres and intermyofibrillar mitochondria (IF) distributed among the myofibrils. It has been suggested that the former support the transport of

substances across the sarcolemma, while only the latter are directly involved with muscle contraction (James &

Meek,1979; Salamonski & Johnston,1982).

In mammals the internal structure of the mitochondria (cristae) appears unrelated to either mitochondrial type (IF or SS) or to fibre type, and the distribution of IF and SS mitochondria is roughly equal (Hoppeler et al, 1981a). In fish this is not the case; there are differences in IF mitochondrial packing between fast and slow fibres

(Johnston,1982b; Egginton & Johnston,1982 b ; Fitch et al,1984: plate4 .5 e ,f ), and there does not seem to be the same sort of grouping of SS mitochondria adjacent to the

capillaries as seen in mamnals (Hoppeler et al,1981a: plate 4.2) .

It may be more functionally relevant to match total

mitochondrial volume rather than mitochondrial volume density to the oxygen consumption cf a muscle, but absolute muscle masses and proportions of red to white muscle are unknown for Antarctic species, so it is difficult to estimate absolute

volumes of mitochondria.

As N .neglecta grows there is an increase in the total oxygen requirement possibly related to an increase in the total volume of mitochondria (a similar ocurrence is seen in mammals; Mathieu et al,1981), although weight-specific oxygen

consumption will decrease with size (Prosser,1973b). There is no correlation between increasing body size and capillary

density for N .neglecta (Fig. 4.3) so this increased total oxygen requirement may be met by increasing the total

capillary numbers. At the same time the mitochondrial density is decreasing (Fig. 4.4). On the whole, Antarctic fish seem well equipped to overcome any handicap caused by the reduced haemoglobin levels; in fact, far from being sluggish and

torpid, some species (including representatives of the icefish family, e.g. Champsocephalus gunnari) are active pelagic

predators (Permitdn & Tar verdie va,1978).

It must be concluded that the design of the respiratory system of Antarctic fish is ably matched to their functional requirements.

SPECIES AREA DENSITY Sv(c,f) Vv(c,f) (um^) {mm ^ ) (cm ^ ) Eel (1) (Anguilla anguilla) 14 2364 379 0.036 Crucian carp (2) (Carassius carassius) 20 1639 312 0.034 African catfish (3) (Clarius mossambicus) 20 1899 398 0.043 Tench (3 ) (Tinea tinea) 22 5092 1106 0.120 Icefish (4) (Chaenocephalus aceratus) 64 544 198 0 . 035 Kotothenia neglecta (Mature) 55 237 79 0.013

Weights(gm), Means + SEM. Eel: 0.14 +/- 0.1; Carp: 16.1 +/- 1.2; Tench: N.D. ; Icefish: 1040 +/- 175; N .neglecta: 900 +/- 50.

Abbreviations: Sv(c,f) - Surface density of capillaries per unit fibre volume;

Vv(c,f) - Volume density of capillaries per unit fibre volume.

References : (1); Egginton & Johnston,1982. (2 ); Johnston & Bernard,1984. (3); Johnston & Bernard

SPECIES CROSS-SECTIONAL AREA MEAN WEIGHT + SEM REF