Guillermo Román

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.

SUSPENSION CULTURE OF THE GREAT SCALLOP Pecten maximus IN GALICIA, NW SPAIN: INTERMEDIATE SECONDARY CULTURE FROM JUVENILES TO YOUNG ADULTS

Abstract A strategy for producing juvenile Pecten maximus to a suitable size for final culture (≈20–60 mm shell-height) within a year is suggested. Effects of stocking density, fouling on cages and shells, and handling frequency (every 1, 2, or 3 mo) on scallop growth and survival were investigated. Small juveniles (16.8 ± 3.0 mm) were initially stocked in August at densities of 24, 36, and 48 scallops quarter−1 (17% to 34% coverage), and 35.5 ± 5.1 mm scallops were restocked in January to 6, 12, 18, and 24 quarter−1 (18% to 73%). Survival was neither affected by stocking density nor handling, and was 98% the first period and from 93.2% to 96.9% between January and July. Shell-growth was mainly affected by stocking density and less affected by handling frequency. Growth slowed down during the winter months, and stocking density influenced growth during all seasons. Juveniles kept at the lowest densities obtained highest growth. Final mean shell-height was 54.8–67.2 mm and coverage 22% to 165%. Scallops handled monthly and bimonthly had significantly larger sizes than scallops handled every three months. Fouling on the cages increased with rising sea temperature, whereas high stocking density significantly reduced fouling on cages. Effective production during intermediate secondary culture in Galicia should include high initial stocking density in August, restocking to low density in January, and changes or cleaning of cages every second month.

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.

Growth of the queen scallop (Aequipecten opercularis) in suspended culture: influence of density and depth

Abstract The effects of density and depth on the growth of juveniles of Aequipecten opercularis held in suspended culture for 11 months in the Ria de Arosa (Galicia, NW Spain) were studied. The densities were 25, 50 and 100 spat per tray (200 to 800 spat m −2 ), and depths were 2, 7 and 12 m. Density and depth were found to affect growth. Although maximum growth occurred at 25 scallops tray −1 , the growth recorded at densities of 50 and 100 scallops tray −1 was only slightly lower. Therefore, on a commercial scale, culture using the higher densities is recommended. There was less growth at 2 m than at 7 and 12 m, due to the surface layers having lower salinities during winter, higher temperatures during summer and lower concentrations of chlorophyll a throughout most of the year. Most growth took place between late autumn and early winter. After 11 months of culture, scallops of initial size 22 mm (shell height) and mean weight of 1.14 g reached a mean size of ≈58 mm and a mean weight of ≈26 g with mortality of less than 5%. The performance of A. opercularis in suspended culture makes it possible to consider this species as a good candidate for aquaculture in the Galician rias, NW Spain.

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.

Relationships among environment, spawning and settlement of Queen scallop in the Ría de Arosa (Galicia, NW Spain)

This study examines the relationship of the reproductive and reserve storage cycles and spat settlement of the Queen scallop (Aequipecten opercularis) to environmental factors. The possibility of farming this species from spat settled on collectors is considered. The gonad condition index shows maximum values between mid-May and early August. Another peak occurs in mid-November. In spring and summer, the energy needed for gametogenesis is derived from food, although it is possible that direct transfer may occur from the digestive gland to the gonad. The glycogen and lipid content of the reserve organs reaches maximum values between late summer and early autumn. The energy requirements related to gametogenesis, which begins in autumn, involve the consumption of accumulated reserves with the resulting reduction in the condition indices. There is a positive correlation between temperature and the condition indices of the digestive gland, the adductor muscle and their lipid and glycogen content, respectively. Two settlement periods were recorded, one in winter, which could not be associated with the spawning of the experimental animals, and another in summer, which coincided with the spawning that took place in spring. The reduced gonad indices recorded at the end of the summer and in winter did not lead to settlement.

Growth and mortality of the king scallop grown in suspended culture in Málaga, Southern Spain

Growth and mortality of the king scallop, Pecten maximus, werecompared when grown in cages and by ear hanging in suspended culturein Fuengirola, Malaga, in southern Spain. Seed (juveniles) used in theexperiment was collected in September 1997 that had settled on collectorsin April-June, of that year. Culture in suspended cages began in January1998 when the seed measured 42.7 (3.3) mm shell height and ended inFebruary 1999. Significantly faster growth was found at a minimum culturedensity (16 scallops/cage) than at two other densities (24 and 36scallops/cage). Depth (1, 5 and 10 m from the bottom) influenced growth,poorest growth occurred closest to the bottom. Under optimum growingconditions, 16 scallops/cage suspended 10 m from the bottom, scallops grewto 10 cm shell length (legal size) by February 1999.In ear hanging culture, ropes were moored in April (51.3 (4.5) mm),June (58.2 (4.5) mm) and November 1998 (64.3 (4.9) mm).Initially, rapid shell growth was observed in all three cultures.Subsequently, the shells became covered with barnacles, Balanus sp.,that possibly caused total mortality of the April culture and led to highmortalities in the two other cultures.

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.