Effect of diet on growth rate and reproductive fitness of Turbo sarmaticus(Mollusca : Vetigastropoda : Turbinidae)

Experiments were conducted to determine the effect of four algal diets (Cor allina spp., Gelidium pristoides, Ulva rigida and an equal volume mixture o f these seaweeds) on growth and reproduction of the South African gastropod Turbo sarmaticus Linnaeus, 1758. The best growth rate of juveniles (up to 13.8 mm shell length and 34.26 g wet body weight increase in 12 months), re productive fitness of mature specimens (gonad index up to 33%) and energy r eserves (up to 4.76 mg glycogen/100 mg foot tissue) were achieved when T. s armaticus was fed U. rigida or a mixed diet. In addition, the gonad index o f individuals fed these diets was almost twice that of similar-sized field specimens. Juveniles fed Corallina spp. only, grew very little (only 2.4 mm shell length and 4.23 g wet body weight increase in 12 months). The reprod uctive fitness of adults fed on such a diet was also poor (gonad index <4.5 %) and energy reserves were low (<3.5 mg glycogen/100 mg foot tissue). Alon g the southeastern coast of South Africa, T. sarmaticus has a distinct repr oductive cycle with gametogenesis occurring from March/April until August/S eptember, whilst maturity (gonad index = 15%) was maintained until December , after which spawning occurred until March.