Contribution to the reproduction of Ruditapes decussatus in Oualidia lagoon and Dakhla bay (North West African Atlantic Coast)

• ¹ Mohammed V University, Biology department, Morocco
• ² Institut National de Recherche Halieutique (INRH), Fisheries Department, Morocco
• ³ Institut National de Recherche Halieutique (INRH), Morocco
• ⁴ Institut National de Recherche Halieutique (INRH), Aquaculture Department, Morocco
• ⁵ Faculty of science, University Hassan II, Biology Department, Morocco

The European clam Ruditapes decussatus is widely distributed along the coastal and estuarine areas of Northern Africa and Europe representing an important resource income due to its high commercial value. Its deposits are often overexploited which could lead to the depletion of some natural stocks of the species. The purpose of this work was to study the reproduction of Ruditapes decussatus in the main production areas of this species: Oualidia lagoon and Dakhla Bay. Monthly samples of the two populations of Ruditapes decussatus were collected between October 2017 and April 2018. The condition index, the allometry (length and flesh dry weight) and the sex-ratio as well as the temperature were studied. In Oualidia (lagoon system), preliminary results showed that in December 2017 and January 2018, all the individuals collected have an undifferentiated sex which correspond with a resting period. A positive allometry has been observed in two periods during the study, the first one from November to December that could indicate a reserve accumulation period. The second one was in March and April that could coincide with the ripe stage. Moreover, singling out the sex has been determined in February 2018 (Female: 5 %; Male: 12.5%; undifferentiated sex: 82.50%). In April 2018, all the individuals have a determined sex (Female: 44%; Male: 56%). The highest temperature value has been observed in October 2017 (20.74°C), while the condition index showed a bimodal distribution in November 2017 (9.93±1.62) and April 2018 (12.37±2.71). Statistical analysis indicated a significant difference between the condition index during the studied periods (ANOVA; p<0.05). In Dakhla (Marine system), all the collected individuals had a determined sex. The chi-square test displayed no significant difference between the sexes. The highest condition index value has been observed in February 2018 (9.97±1.32), then gradually decreasing reaching its lowest value in April (8.05±1.65). The highest temperature values were observed in October (19.01°C). Our results defined no correlation between the temperature and the condition index (p>0.05). In the Oualidia lagoon we have a three month resting period, that coincides with the decrease of the temperature (≤16°C), while in Dakhla bay no resting period was revealed, which could be due to the richness in terms of nutriment of this region, as well as the presence of a relatively high temperature (≥16°C). Further histological studies are in progress to determine various stages of the gametogenesis cycle, which are essential to establish monitoring programs to better manage and conserve the resources of this species.