The reproductive cycle of the mussel Perna picta (Born) on the Moroccan Atlantic coast near Rabat was studied by perio&c observations of gonadal sections, dry tissue weights, b~ochemical composition and spatfall in a natural population. The sex ratio was 55:45 in favour of males; n~ussels attained sexual maturity at 22 mm shell length in both sexes. The general pattern of gametogenic activity of P. picta was comparable with that of Mytilus spp. reported from temperate regions. Gonad development began in October and the gonads were ripe in January or February. Spawnings and reconstitution of gametes took place several times between February and May, and the gonads entered the resting stage or showed reduced activity in summer (June to September). Recruitment occurred between May and September. As in Mytilus spp. from temperate regions, there was an inverse relationship between carbohydrate and protein in the storage and utilisation cycles of these 2 components. While carbohydrate reserves accumulated in the tissues during periods of gonadal inactivity (summer and autumn), protein was stored during periods of gonad development (winter). Energy values calculated per g ash free dry tissue weight fluctuated between 22.3 and 24.4 kJ and energy content (kJ ind.-') was maximal in winter and minimal in summer

Energy relations of a population of black scallop Chlamys varia (L.) in Lanveoc (Bay of Brest, France) were studied from 1976 to 1978. The population had a production of 538.52 Kcall00 mu' and of 497.10 Kcal 100 m"' during the years 1976 to 77 and 1977 to 78, respectively; it assimilated 5773.21 Kcal 100 m-' during the first year and 4561.21 Kcal 100 m"' during the second year of this study. Net production efficiency of black scallops (9 to 12 %) was very low compared to that of other bivalve populations reported so far. Average annual biomass of the population studied was 1252.59 Kcal 100 m-2 and 956.06 Kcal during the 2 yr period of study. Considerable energy was eliminated by the population due to mortality (natural and fishing mortality): 1017.42 Kcall00 m 2 and 939.51 Kcal 100 m 2 during the first and second second year, respectively. Average P:B ratios were 0.43 and 0.52 during the 2 yr.

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