JoséL. Sánchez

Seasonal variations in condition, reproductive activity and biochemical composition of the flat oyster, Ostrea edulis, from San Cibran (Galicia, Spain)

The influence of environmental parameters (temperature, salinity and available food) on the condition, reproductive activity and biochemical composition of a native population of Ostrea edulis L. in San Cibran (Galicia, Spain) was studied between September 1988 and December 1989. Histological preparations of gonads showed that gametogenesis started when temperature was at its lowest in winter. The water temperature in San Cibran never fell low enough to interrupt it. Gametogenesis proceeded slowly and spawning took place in May–June, although the predicted time of ripening was early March. Salinity in San Cibran was relatively stable throughout the year; it did not seem to have any influence on gametogenesis. Available food appeared to be a very important factor in controlling gonad growth, once gametogenesis was initiated. The major concentration of suspended organic particulate matter was present in the spring at the time of rapid gonadal maturation. Only one spawning period was observed. Larvae were released when the food in the water was high. Seasonal changes in the main biochemical components of this oyster were determined for a standard individual. Lipids and carbohydrates presented a similar time-course whereas proteins were constant. When food was abundant, energy reserves were built up. Spawning produced a decrease in biochemical constituent levels, and recovery coincided with the phytoplankton bloom. The stored reserves, mainly lipids, were used to overcome a state of energy imbalance in late autumn associated with low food availability. Results show this oyster to be an opportunist organism which concentrates its reproductive effort during a short period of favourable conditions and which is directly dependent on nutritive availability in the environment.

Seasonal changes in condition and biochemical composition of the scallop Pecten maximus L. from suspended culture in the Ria de Arousa (Galicia, N.W. Spain) in relation to environmental conditions

Abstract Seasonal changes in condition and biochemical composition of striated adductor muscle, digestive gland and female gonad of raft cultured Pecten maximus L. in the Ria de Arousa (Galicia, N.W. Spain) were studied over 16 months in relation to environmental conditions and reproductive events. Pecten maximus in the Ria de Arousa showed a clear cycle of energy storage and utilisation. Between March–April and October carbohydrates and proteins were accumulated in the striated adductor muscle and lipid in the digestive gland. From October to March of the following year there was a loss of such energy reserves. In the ovary there were two annual periods (winter and spring) of increase in the energy content owing to the gonad recovery, which were characterised mainly by the rise in the percentage of lipid. This correlated positively with the gonad condition index and with the mean diameter of the oocytes. The energy necessary for the gametogenesis in late autumn and winter (from October to March) was supplied by the reserves of the striated adductor muscle and the digestive gland; the energy provided by the adductor muscle was double that supplied by the digestive gland. Part of this energy was also used to support the basic metabolic maintenance requirements. The contribution to the energy loss (from October 1990 to March 1991) of the striated adductor muscle carbohydrate and protein and digestive gland lipid was similar (32.45, 27.06 and 29.15 kJ respectively). In spring the gametogenesis took place at the expense of the available food which was also sufficient to allow concurrent energy storage in the adductor muscle and the digestive gland.

Seasonal variations of the lipid content and fatty acid composition of Crassostrea gigas cultured in E1 Grove, Galicia, N.W. Spain

Lipid classes and fatty acids of triacylglycerol and phospholipid fractions of introduced Crassostrea gigas from E1 Grove were analysed and compared for 16 months. The fluctuations in the lipid content were correlated to the phytoplankton concentration and sexual cycle. The seasonal variations in lipid content were due largely to changes in triacylglycerols, the major lipid class. Phospholipids and sterols followed a similar seasonal cycle with minor oscillations. Polyunsaturated fatty acid (PUFA) was negatively correlated with temperature and showed a pattern similar to n-3 series with great fluctuations, whereas the n-6 fatty acids had minor fluctuations throughout the year and showed no clear seasonal variation. The content of 20:5n-3 was higher than 22:6n-3 in triacylglycerols and similar in phospholipids. The 20:4n-6 was the major fatty acid of n-6 series and correlated negatively with condition index, temperature and chlorophyll a in the phospholipid fraction. The maturity index correlated positively with 18:4n-3 from phospholipids.

Seasonal variations of lipid classes and fatty acids in flat oyster, Ostrea edulis, from San Cibran (Galicia, Spain)

Abstract Lipid class analyses and fatty acid composition of triacylglycerols and phospholipids were carried out in a wild population of Ostrea edulis over a period of 16 months. Phospholipid was the most abundant class except in September 1989. The low level of triacylglycerols suggests a scanty food availability. The seasonal cycle of phospholipids, triacylglycerols and free sterols was parallel to that of total lipids. Close to two-thirds of triacylglycerol fatty acids were polyunsaturated (61.8 ± 6.45%). It is suggested that this lipid class may act as a temporary reservoir of important polyunsaturated fatty acids. Both triacylglycerols and phospholipids were highly unsaturated because of large concentrations of n-3 polyunsaturated fatty acids (PUFAs). The percentage of n-3 PUFAs was always higher than n-6, and n -3 n -6 was considerably elevated. The possible deficiency of essential fatty acid seems to be compensated by a relatively high proportion of 20:3n-9 fatty acid and non-methylene-interrupted fatty acids. The results reported in this paper appear to show a poor nutritional condition.

Energy metabolism of newly settledOstrea edulis spat during metamorphosis

An energy budget for metamorphosis in oyster spatOstrea edulis L., collected in the Instituto Español de Oceanografía during March–April 1988, was determined. The energy cost of metamorphosis was calculated from measurements of biochemical components which form the principal reserves of energy and which are used significantly during metamorphosis. The results indicated that protein supplied most of the energy inO. edulis spat. The idea that neutral lipids were used selectively as an energy reserve during the metamorphosis of this bivalve marine larvae was questioned.

Influence of the gametogenic cycle on the biochemical composition of the ovary of the great scallop

The oogenic cycle and biochemical composition of the ovary of raft-cultured great scallop (Pecten maximus) were studied during the period April 1990–July 1991. The ovary condition index (FGI) and stereological studies showed the existence of two principal spawning periods, winter and late spring-early summer. No sexual resting period was found. Oocyte lysis was high throughout the year. Ovarian lipid levels displayed a clear seasonal pattern linked to the gametogenic cycle. Total lipid (TL, 16–21% dry weight), acylglycerol (AG, 20–65% TL) and free sterol (FS, 2.8–6.4% TL) levels were, generally, higher in the ripe ovary and a decrease coincided with spawning. Protein (59–63% dry weight), glycogen (<3% dry weight) and phospholipid (PL, 26–35% TL) levels showed no clear seasonal trend. The TL and AG were a good index of ovarian sexual maturity. The TL % of dry weight) correlated well with the female gonad condition index (rs = 0.779, p < 0.001), and AG (% f TL) correlated well with the mean oocyte diameter (rs = 0.630, p < 0.01) and the female gonad condition index (rs = 0.443, p < 0.05).

The regulation of glycolysis in the hepatopancreas of the sea mussel Mytilus edulis L.

Abstract 1. 1. Hepatopancreas contents of glycolytic intermediates were determined in Mytilus edulis L. under different conditions and mass-action ratios for several reactions were calculated. 2. 2. Phosphofructokinase, fructose diphosphatase, pyruvate kinase and, likely, hexokinase appeared as non-equilibrium enzymes. 3. 3. The changes of intermediate contents are discussed in relation with the expected changes of glycolytic or gluconeogenic flux. 4. 4. Direct evidence was obtained favouring a regulatory role of pyruvate kinase and the system phosphofructokinase/fructose diphosphatase in mussels.

Growth of clam seed (Ruditapes decussatus) reared in the wastewater effluent from a fish farm in Galicia (N.W. Spain)

The use of the effluent from an intensive culture of turbot, Psetta maxima, cultured at Nastos (Galicia) as a source of nutrients for growing the Ruditapes decussatus seed was evaluated and compared with the growth under field conditions in a clam-rearing zone (Carril, Galicia). The seed was placed at a density of 2.5 kg/m2 in trays suspended in four tanks with different flow rates. Wastewater was changed at the rate of 1 vol./h, 2 vol./h and 4 vol./h. The fourth tank with sea water was the control. In Carril, the seed was planted at a density approaching 2 kg/m2. After 60 culture days, the slowest growth rate was in the control (K = 0.001) and the fastest in 4 × h tank (K = 0.0363), with mortality rates less than 18% whereas in Carril, it was approximately 35%. Significant (P < 0.05) differences of weight and length existed between successive samplings but not between the three different flow rates. The condition index in the experimental tanks was similar ranging from 13 to 19. In Carril, the seed reached a similar weight to that registered in the 1 × h and 2 × h tanks, although the shell length and the condition index were less. At the end of the experiment, all biochemical component levels (mg/individual) were higher in the clams fed with the wastewater, mainly neutral lipids (45.8 μg/mg DW), whereas the clam cultivated in Carril presented a high concentration of carbohydrates, mostly as polysaccharides (84.3 μg/mg DW). The clams prefattened with the wastewater also had the greatest energy content (803.1 J/individual) compared to the low values registered in the control tank and Carril (maximum of 233.0 and 304.8 J/individual, respectively). Only minor differences were observed in the fatty acid spectrum of the seed reared in the tanks or in Carril.

Biochemical composition and fertilization in the eggs of Mytilus galloprovincialis (Lamarck)

Abstract The biochemical composition of eggs spawned from mussels Mytilus galloprovincialis (Lamarck) collected from Galician Rias (Spain) is, in general, similar to that indicated for other marine molluscs. Proteins (45% of total dry weight) and lipids (22%) are the main reserves of the egg while carbohydrates (3%) are the lowest constituent. Egg diameter showed a mean value of 61 μm and egg density followed an unimodal distribution of frequencies with a mean value of 1.057 g · cm −3 . Fertilization of the eggs of M. galloprovincialis can be delayed for about 4 to 8 h after spawning over the temperature range of 10 ° to 18 °C. After these times, percentage of fertilized eggs decreased to less than 30%. At 18 °C the low values in successful fertilization may be due to the degradation of the eggs. A delay in addition of sperm after release of the eggs increases the time in which first cell cleavage appears from the moment of insemination. Variation of the biochemical composition of unfertilized eggs over time was also studied. At 18 °C proteins, lipids and carbohydrates decreased by about 45, 46 and 48%, respectively, after 5 h (only 4% of total eggs were fertilized) from spawning. At 10 ° and 14 °C the decreases after 11 and 8 h from spawning, respectively, were lower. Before these times, the decrease of biochemical constituents was not so great and fertilization rates were still high.

Sterol composition of gonad, muscle and digestive gland of Pecten maximus from Málaga (South Spain)

Sterol composition and content and their seasonal variations over 18 months were investigated in adductor muscle, digestive gland and gonads of Pecten maximus. Sterols were isolated by Silicagel 60 thin layer chromatography and identified by gas chromatography/mass spectrometry. Eleven sterols were identified, with cholesterol, brassicasterol, 24-methylenecholesterol and 22-trans-dehydrocholesterol being the principal components. The same sterols were found in all three tissues independent of season. The relative amounts of each sterol present in each tissue differed. Total sterol levels in gonad and muscle were higher than in digestive gland. Statistically significant differences (P<0.05) were found between the concentrations of each of the sterols isolated from the gonad or muscle and digestive gland. The seasonal variations in the sterol content of the gonad seem be related to the reproductive cycle, while the sterol content of the digestive gland appears to be linked to diet, mainly diatoms or dinoflagellates. The muscle sterol content showed minor changes throughout the year.