Antonio J. Pazos

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.

Lipid classes and fatty acid composition in the female gonad of Pecten maximus in relation to reproductive cycle and environmental variables

Abstract Lipids in the female gonad of Pecten maximus from Ria de Arousa (N.W. Spain) were analysed for lipid class composition and fatty acid composition of triacylglycerols and phospholipids and their variations in relation to gametogenic cycle were studied for 16 months. The female condition index and stereological studies showed the existence of two principal spawning periods, winter and late spring-early summer. No sexual resting period was found and oocyte lysis was high throughout the year. Ovary lipid levels (16–21.5% dry weight) displayed clear seasonal changes linked to the gametogenic cycle. The acylglycerols (20–65% total lipids)and phospholipids (26–35%) were the major lipid classes, sterols (4–8%) were present in minor amounts. The acylglycerols and free sterols showed a seasonal variation similar to that of the mean oocyte diameter. The remainder of lipid classes showed no clear seasonal variation. The 20:5n-3 levels were higher than that of 22:6n-3 in the triacylglycerols, contrary to that of phospholipids. The polyunsaturated fatty acids (PUFA) were more abundant in the triacylglycerols and the series n-3 was clearly predominant. The Σn-3 and the principal n-3 fatty acids (mainly in phospholipids) showed a seasonal variation clearly related to the reproductive cycle.

Seasonal changes in lipid classes and fatty acid composition in the digestive gland of Pecten maximus.

Seasonal variations in lipid classes and fatty acid composition of triacylglycerols and phospholipids in the digestive gland of Pecten maximus were studied over a period of 16 months. Acylglycerols predominated (19-77% of total lipids), in accordance with the role of the digestive gland as an organ for lipid storage in scallops. Seasonal variations were mainly seen in the acylglycerol content, while phospholipids (2.5-10.0% of total lipids) and sterols (1.9-7.4% of total lipids) showed only minor changes. The most abundant fatty acids were 14:0, 16:0, 18:0, 16:1(n-7), 18:1(n-9), 18:1(n-7), 18:4(n-3), 20:5(n-3) and 22:6(n-3) and these showed similar seasonal profiles in both, triacylglycerol and phospholipid fractions. In contrast to the phospholipid fraction, the triacylglycerol fraction contained more 20:5(n-3) than 22:6(n-3). In three phospholipid samples we noted a high percentage of a 22-2-non-methylene-interrupted fatty acid, previously described to have a structural role in several bivalve species. The main polyunsaturated fatty acids displayed important seasonal variations parallel to those of the acylglycerols, suggesting good nutritional conditions. A positive correlation existed between the level of saturated fatty acids and temperature, whereas the levels of polyunsaturated fatty acids correlated negatively with temperature.

Stereological studies on the gametogenic cycle of the scallop, Pecten maximus, in suspended culture in Ria de Arousa (Galicia, NW Spain)

Abstract Samples of Pecten maximus cultured using the ear-hanging technique were collected at regular intervals from April 1990 to July 1991. The gametogenic cycle has been studied in relation to the environmental conditions (temperature, chlorophyll a and seston) and assessed by two different methods: determination of the gonad condition index and study of the oocyte diameter by image analysis following a Stereological technique. Two principal spawning periods were found, the first one in late spring and early summer (May–June 1990, June–July 1991), the second one in winter (February–March 1991). The temperature ranges from 11 to 21 °C with maxima in July and minima in December. Low temperatures during maturation gave rise to a delay in the spawning period. Spring spawning appears to occur after a threshold temperature around 16 °C is reached, whereas winter spawning takes place at lower temperatures (12–13 °C) and can be triggered by a phytoplankton bloom. Minor spawnings may be possible in late summer and at the beginning of autumn. No sexual resting period exists. The number of atretic oocytes were very high throughout the year. Oocyte lysis appears to be a common process linked to the reproductive strategy.

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).

Settlement Behavior of Black Scallop Larvae (Chlamys varia, L.) in Response to GABA, Epinephrine and IBMX

Abstract Competent larvae of the black scallop Chlamys varia (L.) were treated with the neurotransmitter gamma-amino-n-butyric acid (GABA), the catecholamine epinephrine, and 3-isobutyl-1-methylxanthine (IBMX), at different concentrations and times of exposure, to test the effects of exposure to the compounds on larval settlement. After 24 h, maximum percentage of settlement (>30%) was induced by 10−5 M epinephrine. After 48 h, maximum settlement rate was also achieved by 10−5 M epinephrine (>54%). Exposure to 10−6 M epinephrine and to 10−6 M GABA also induced significantly higher larval settlement than in control larvae. By contrast, IBMX failed to induce significantly higher settlement rates than in the control larvae. Epinephrine and GABA were identified as active inducers of settlement in C. varia, and were not toxic to black scallop larvae. This is the first report in which the involvement of epinephrine and GABA in the settlement of C. varia larvae is described.

Effects of Temperature Regime on Broodstock Conditioning of Ruditapes decussatus

Abstract To optimize the conditioning procedure to obtain better larvae with lower production costs, Ruditapes decussatus broodstock was conditioned at different periods during the year [October (C1), February (C2), and April (C3)] under two different controlled temperature regimes: a constant temperature (CT, 20°C) and a gradual increase in temperature from ambient to 20°C (GT). Samples (30 adult clams) were collected randomly every month from a control group and from each conditioning tank (three tanks for each temperature treatment). A section of the gonad-visceral mass was sampled for gonadal histology and the remaining tissue was used for biochemical analyses. Gonadal developmental stages were determined based on the classification proposed by Wilson and Seed (1974), and fertilized eggs were reared after the method of Walne (1966). In the three conditioning experiments fewer degree-days were required to successfully spawn clams in tanks with the gradual increase of temperature. Clams conditioned in October spawned in February, four months prior to spawning under natural conditions after 1,030 degree-days (D°) in CT tanks and 937.5 D° in GT tanks. Clams conditioned in February and April spawned after 410 D° and 470 D° when held at constant temperature respectively, whereas a gradual increase of temperature shortened this to 383 D° and 337.5 D° respectively. The most important difference between the two temperature regimes was the higher condition index of clams conditioned under the GT regime. The percentage of larvae that survived metamorphosis was higher in clams conditioned at GT, maximum survival ranged from 25% in C3 at CT to 40% in C1 at GT, except for CT tanks in C2 where it was less than 10%. Results showed that Ruditapes decussatus conditioned with a gradual increase in temperature, enhanced larval production and also reduced overall hatchery production costs.

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.

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.