ISSN: 0001-5113 ACTA ADRIAT., ORIGINAL SCIENTIFIC PAPER AADRAY 57(1): 93 - 106, 2016 Broodstock conditioning and gonadal development of the smooth clam Callista chione (Linnaeus, 1758) (Mollusca: Bivalvia) on the Catalan coast (NE Spain) Marina DELGADO1*, Josu PÉREZ-LARRUSCAIN2 and Joan IGNASI GAIRÍN2 1Instituto Español de Oceanografía. Centro Oceanográfico de Cádiz. Muelle de Levante s/n, P.O. Box 2609. E-11006 Cádiz (Spain) 2Institut de Recerca i Tecnologia Agroalimentaries (IRTA). Centre de Aqüicultura. Carretera del Poble Nou, Km 5.5. E-43540 Sant Carles de la Rápita, Tarragona (Spain) *Corresponding author, e-mail: [email protected] In order to select the most suitable broodstock conditions for Callista chione, a conditioning experiment was performed and the gametogenic cycle of a natural population on the coast of Arenys de Mar (Catalonia, NE Spain) was studied. The influence of food availability and sand bed presence on energy balance and gonadal development was analyzed, also the proliferation of intracellular bacteria in gills was monitored. The gametogenic cycle started between August and September. In November, most of the gonads were ripe and spawning began in December. The higher abundance of spawning clams occurred between January and April (with sea surface temperature 13-15ºC). Three experimental conditions were tested in September at a constant temperature of 14ºC:T1 (0.10% of organic weight of microalgae as a proportion of the live weight of the clams per day and a sand bed); T2 (0.05% and a sand bed); T3 (0.10% without a sand bed). Gonadal maturity was a priority for this species and was reached at the end of all trials. Food availability and sand bed presence benefit survival and gonadal development. The best results were obtained in clams from trial T1. Nevertheless, broodstock conditions seemed to trigger the proliferation of intracellular bacteria in gills, and as the experiment advanced, prevalence and intensity of infection increased for all trials reaching values of 100% and between 9-40 intracellular bacteria/pair of gill plica, respectively. Key words: Callista chione, reproduction, temperature, food availability, sand, gills, histopathology INTRODUCTION the Catalan coast (DOGC, 2008). Catches have dramatically decreased over the recent years, The smooth clam Callista chione (Linnaeus, threatening the biological and economic sustain- 1758), is distributed on sandy bottoms through- ability of this fishery along the natural beds of out the Mediterranean Sea and European Atlan- the Catalan coast (DOGC, 2008). This decline in tic coasts over 0-180 m depth range (SALAS, catches and the interest in diversifying aquacul- 2011). This species is of great commercial inter- ture, have led to the development of a program est in Spain, and is intensively exploited along of investigation into the management in hatch- 94 ACTA ADRIATICA, 57(1): 93 - 106, 2016 eries of this species through projects carried temperature or diet on gonadal development out in different Spanish geographical locations (PÉREZ-CAMACHO et al., 2003; DELGADO & PÉREZ- (JACUMAR). CAMACHO, 2007; OJEA et al., 2008). The influence Most of the biological information currently of other environmental variables on energy bal- available, proceeds from studies carried out in ance or gonadal development has not been stud- the natural environment, and several studies ied. Specifically, the burrowing in substratum have already described the reproductive cycle of bivalves has not yet been widely studied or of this species (VALLI et al., 1994; TIRADO et al., related to physiological aspects despite the fact 2002; MOURA et al., 2008). These studies reported a that this is the normal condition of most of these prolonged reproductive cycle with three spawn- organisms in the natural beds. Growing burrow- ing peaks and the absence of a resting period ing molluscs under non-natural conditions could in SE Spain and southern Portugal. However, potentially cause physiological stress (BOSCOLO despite commercial interest, no detailed infor- et al., 2003), shell deformities and/or behavioral mation about reproductive aspects of C. chione changes (LAVALLEY, 2001). In contrast, EPEL- has been reported in the NW Mediterranean Sea. BAUM et al. (2011) suggest that the addition of This information is not only necessary to imple- substratum may have an indirect effect on clams ment fisheries management measures but also to through increasing the three-dimensional space select the most appropriate period of the year for available to them which, in turn, could increase carrying out broodstock conditioning. growth and survival by reducing physiological Environmental parameters determine to a stress. great extent the dynamics of growth and repro- In spite of commercial interest, only two duction of bivalves (GABBOTT & BAYNE, 1973). conditioning experiments at 18ºC have been car- Temperature and food availability have been ried out (DELGADO et al., 2007; MARTÍNEZ-PITA et identified as playing a major role in the evolution al., 2011). DELGADO et al. (2007) described the first of the reproductive cycle (SASTRY 1979; BAYNE & conditioning experiment of adults and reported NEWELL, 1983). Temperature is normally respon- severe mortality events associated with the pres- sible for initiating gonadal development and an ence of branchial intracellular bacteria, histo- increase in temperature speeds up most of the logically designated as rickettsia-like organisms. physiological processes, including clearing and The presence of these intracellular bacteria was ingestion rates as well as respiration and growth detected in the sample from the natural beds (GRIFFITHS & GRIFFITHS, 1987). On the other but strengthened under broodstock conditions. hand, previously stored food reserves or food The level of intensity of the infection probably supply also plays an important role in the suc- affected respiration and ingestion rates and, con- cess of reproduction determining the extension sequently, increased mortality rates. of the reproductive process (LUBET, 1959; NAVAR- In order to select the most suitable brood- RO et al., 1989) or the rate of gonadal development stock conditions for C. chione, our main objec- (RUIZ et al., 1992; DELGADO & PÉREZ-CAMACHO, tive was to study the influence of food availabil- 2003). Other authors have described the nega- ity and sand bed presence, at a lower condition- tive effects of food shortage on the reproductive ing temperature (14ºC), on energy balance and output of certain species such as Mytilus edulis gonadal development as well as to determine (GABBOTT & BAYNE, 1973). In all cases, both vari- their influence on the proliferation of intracel- ables interact and determine the acquisition and lular bacteria in gills. The reproductive cycle expenditure of energy available for reproduc- in the natural beds was also studied in order to tion and/or somatic growth (DELGADO & PÉREZ- adjust the beginning of the conditioning trials CAMACHO, 2007). to a suitable gametogenic stage and define the Broodstock conditioning experiments on proper conditioning temperature. venerid species usually test the influence of DELGADO et al.: Broodstock conditioning and gonadal development of the smooth clam Callista chione ... 95 MATERIAL AND METHODS Broodstock conditioning: Design and experimental conditions Analyses and visualizations of remote-sens- ing data observations of sea surface temperature The conditioning experiment was performed and chlorophyll-a concentration used in this in September in the laboratory (IRTA hatchery; study were produced with the Giovanni online Fig. 1). In this month most of the clams in the data system, developed and maintained by the natural bed on the Catalan coast (NE Spain) (> NASA GES DISC (Ocean color radiometry 70%) were in suitable stages of gonad develop- online visualization and analysis). ment to start a new gametogenic cycle (stages 1 Samples of C. chione were collected by and 2) Due to the fact that a temperature of 18ºC dredging off the coast of Arenys de Mar (Cata- could be a stress factor (DELGADO et al., 2007), lonia, NE Spain; 41º34’N, 2º35’E) (Fig. 1). For and the coincidence of the maturation period each individual, the shell length (maximum with temperatures around 14ºC in these natural distance along the anterior-posterior axis of the beds (see Results section), our objective was to shell, SL) was measured to the nearest 0.1 mm test using 14ºC as the conditioning temperature. with a digital caliper. Live weight (LW) was Moreover, the effects of two contrasting condi- also recorded for each specimen to the nearest tions of food availability were examined at this 0.001 g. temperature as well as the presence of sand substrate that would allow clams to burrow. A Reproductive cycle histopathological monitoring of gills was also carried out for all experimental conditions. The reproductive cycle in the natural beds The experiments were performed in a flow- of Arenys de Mar was studied to adjust the through system containing seawater filtered beginning of broodstock conditioning trials to through 1 μm mesh and maintained at a constant a suitable gametogenic stage and to define temperature (14ºC) and salinity (33%). The the proper conditioning temperature. A natural initial number of specimens was 70 for each population of C. chione was monitored over experimental condition (45.13 ± 7.37 mm SL). one year (January–December 2008). Samples As a consequence of the large number of indi- were collected monthly in the natural beds off viduals used in each experiment and the long the coast of Arenys de Mar at a depth of 5-30 m duration (58 days) of the surveys, clams were (Fig. 1). Given that species size at first maturity kept in large groups in 25 liter plastic tanks. In is estimated to 30 mm SL for the littoral area of this way, food concentration was more stable and equal for all clams at each experimental Catalonia (GALIMANY et al., 2006), approximately 20 individuals (> 38 mm SL) were collected stage and was closer to natural conditions. The monthly in order to study the gametogenic cycle design of this experiment was similar to the one by means of histological techniques.