Plasma glucose and plasma fatty acid levels of Limanda limanda (L.) in relation to season, stress, glucose loads and nutritional state

Abstract

The effects of season, stress, glucose loads and nutritional state on the plasma glucose (PG) and plasma fatty acids (PFA) of Limanda limandu were examined. Plasma glucose levels showed no seasonal variation while PFA exhibited two peaks during May to August, and in December respectively. These peaks may be associated with resorption of gonadal material after spawning and the mobilization of lipid reserves for vitellogenesis. Lirnandu showed a hyperglycaemic response to a brief aerial emersion, followed by a hypoglycaemic condition. Infusion of a glucose load and the ingestion of a satiation meal ofA4ytilu.s edulis tissue led to a reciprocal rise and fall of PG and PFA. Short-term food deprivation had no effect upon PG although PFA rose significantly.

Determinants of otolith chemistry seasonal variation in the composition of blood plasma, endolymph and otoliths of bearded rock cod Pseudophycis barbatus

“…Fletcher (1984) and White e t al. (1986) obtained the opposite result, and attributed increases in plasma phospholipids after spawning in Limanda limanda and Pleuronectes platessa to the reabsorption of ovarian material which is predominantly lipid, specifically phospholipid.…”

“…In each of these 2 studies the blood glucose levels were measured in fish which had been maintained in captivity without feeding for at least 1 wk. Fletcher (1984) found that feeding dramatically increased plasma glucose in Limanda limanda to more than 6.4 mM I-' in summer and 3.4 mM 1-' in winter The effects of feeding were evident almost immediately and the plasma glucose levels remained elevated for up to 50 h. Bergot (1979) found that plasma glucose levels reached their peak in rainbow trout 6 h after a glucose-enriched meal. Because the majority of the cod used in this study were collected between 11:OO and 14:OO h, ca 5 to 8 h after first light, when feeding probably commences, high plasma glucose levels would be expected.…”

“…Wardle (1972) estimated normal blood glucose levels in adult plaice Pleuronectesplatessa as 0.8 to 1.4 mM 1-l, and White & Fletcher (1985) found levels varied seasonally from about 0.8 to 2.0 mM I-' for the same species. Fletcher (1984) found that plasma glucose levels remained between 1 . l and 1.4 mM I-' and did not vary seasonally 50K and 100K, probably albumin.…”

“…He did not consider the relative glucose levels of fish in the fed and unfed state. In addition to capture-related stress, it is important to consider environmental stress (Wedemeyer 1981), temperature (Umminger 1969 (Lehninger 1975); this effect is clearly illustrated in research on the sand dab Limanda limanda (Fletcher 1984).…”

“…Lipids, primarily in the form of triglycerides stored in the liver, are mobilized during periods of starvation (Lehninger 1975). In 'fatty' fish species interstitial fat in the muscle tissue may also serve a s a storage site for triglycerides (Larsson & Fange 1977, Fletcher 1984, White et al 1986), but it is only in times of extreme deprivation that cell constituents such as the phospholipids are broken down for use as an energy source (Lech 1970).…”