Seguridad de los equipos

spawning, and in November (2.13) at the end of winter, the latter suggesting that Everson (1970a) was correct in

stating that these fish do not feed as the seals are

returning to the Islands. The condition factor was high and fairly stable throughout the summer months, falling in May and June as more body stores are directed to gonad

development; presumably female fish will tend to be less 'fit' than males, since a larger proportion of the body mass is accounted for by the gonads. Comparison of (Figs. 2.6 & 2.7) shows that CF and RGS parallel each other. For

instance, the relative gonad size in female N.neglecta

rises during the summer months, peaking in May at a value of over 16%. In some species the weight of the genital

(Iles,1971). There was a rapid fall of RGS in June indicating spawning has occurred, then values remained

steady during the winter rising again from November onwards. Immature female fish showed a similar peak in RGS in May (Fig. 2.6) although to a smaller extent than adult females.

A cyclical trend was also seen when comparing the RLS with month (Fig. 2.8). The RLS increased in both female and male fish from June to September, followed by a fall. This also supports the theory that N.neglecta ceases to feed in the late winter months and is utilising it's liver

carbohydrate stores. Identical patterns of RLS varying with month were observed by Everson (1969). This partial-fast is

coincedent with the return of weddell and elephant seals, both of whom consume fish in their diet (Dearborn,1965; Stonehouse,1972). The drop in RLS during the late winter might also be indicative of reduced food supplies, but

Daniels (1982) has pointed out that the feeding strategy of N.neglecta is such that it can consume adequate prey items all the year round. It is possible that although the

quantity of food ingested in the winter is still maintained, the quality of the food may be poorer in the winter leading to a less efficient conversion into energy supplies or

storage materials. There is another fall in RLS just prior to the onset of spawning, that is most evident in the

females (Fig. 2.8). Similar trends were seen in the cod (Gadus morhua), where the energy content of the liver was also measured. In this species the energy content of the liver fell just before spawning as the accumulation of

gonadal material required more energy than could be provided by the diet (Eliassen & Vahl,1982). Since the female gonads

account for such a large proportion of the body weight in ripe fish, they would probably constitute a larger energy demand than the male gonads.

The gross muscle chemistry of N .neglecta was monitored on a monthly basis to see if there was any indication of changes occurring in parallel with those in condition factor. Generally it is very difficult to separate the effects due to the environment from those due to maturation, starvation etc. (Jacquot,1961). However, the marine

environment of the Antarctic is very stable, with water temperatures remaining fairly constant throughout the year

(Fig. 2.1), and despite the peak of primary production that occurs in the austral spring (Foxton,1956) it has already been stated that N.neglecta has evolved a feeding strategy to enable it to maintain it's food intake all the year round

(Daniels,1982). Consequently the major seasonal stress on Antarctic fish would be that caused by gonadal growth and

spawning. If the energy demand associated with reproduction exceeds the energy supplied by the food then the body

reserves must be drawn upon. The seasonal changes in water, protein and lipid contents of the muscle (and liver) have therefore been related to growth of the gonads in several fish species (Love,1970; Shul'man,1974).

Inter-relationships of the main constituents of white muscle during depletion vary considerably in different species according to the location of stored lipid

(Love,1970). 'Fatty' fish such as the mackerel (Scomber scombrus) and herring (Clupea harengus) have high

concentrations of reserve lipid in the muscle tissue, and during times of depletion these are drawn upon first; even

after several months depletion there may still be very little protein breakdown (Inui & Ohshima,1966 ; Love,1970 ). There is therefore, a relationship between the muscle lipid and muscle water content; as the lipid levels fall during depletion, the water level rises (Brandes & Dietrich,1956). In 'non-fatty' fish such as the cod (Gadus mor hua) and the plaice (Pleuronectes platessa) there are less extensive lipid depots in the muscle and the stored lipid is found mainly in the liver. During depletion these species utilise lipid from the liver first and then maintain carbohydrate at the expense of muscle proteins (Butler,1968 ; Renaud &

Moon,1980); thus there is a relationship between muscle protein and muscle water. This relationship is seen better in the white muscle since red muscle proteins are conserved during starvation (Johnston & Goldspink,1973 ; Beardall & Johnston,1983). For example in the plaice, red muscle water content was not significantly different even after 14 weeks starvation although the water content of the white muscle had increased significantly (Johnston & Goldspink,1973).

N.neglecta is classified as 'non-fatty' (Crawford,1979),