Abstract

Dependence on natural stocks is a potential limitation to perform sea urchin fertilization bioassays, both because of limited amounts of gametes (when they are available) and natural seasonal fluctuations in gamete production. Those constraints may be eliminated maintaining animals in the laboratory under proper cultivation procedures and manipulating critical variables. Feeding regime has been shown to be one of such critical variables for increasing gonadic production in sea urchins under cultivation. Since the egg fertilization bioassay is intended to mimic a natural process under man-made stressful conditions, the manipulated feeding regime should be more conveniently based on natural food. The coastal South-Eastern Pacific carnivorous sea urchin Arbacia spatuligera adapts well to aquarium life and its gametes are widely used in toxicity bioassays of water samples during a few months of gonadic ripeness. We tested for food preference in A. spatuligera among a multiple choice of natural food types in short term experiments and subsequently fed stocks of sea urchins under cultivation with the preferred food for a long period. Multiple-choice feeding-preference experiments present some special complications that we address here by introducing paired experimental arenas and statistical analyses based on rank statistics. The sea urchins showed a clear food preference. Females showed increased gametic production while males showed a tendency in the same direction when fed ad libitum with the preferred food item for 1 year under controlled experimental conditions. Although results are encouraging, it remains to be seen if the favourable feeding regime, and possibly manipulation of additional critical variables, allows circumventing the seasonal cycle of gamete production to maintain a constant source of high quantities of gametes of sea urchins under cultivation