2. Material and methods
Ž Mature scallops obtained from Culture Centers in Tongoy Bay Region IV, North of
. Chile
were induced to spawn by increasing the temperature and adding excess
Fig. 1. Gonadosomatic indexes of A. purpuratus broodstock during conditioning with different diets at 16 8C
and 20 8C. Microalgae–CHO: mixture of microalgae and carbohydrates; Microalgae–lipids: mixture of
Ž .
Ž .
microalgae and lipids. First experiment 1997 . MeansS.E. N s 3 are shown.
microalgae. The spent animals were distributed among 18 tanks which were divided into two groups and placed in separate temperature-controlled laboratories, one at 16
8C and the other at 20
8C. Three groups in each laboratory were fed with a mixture of Ž
. microalgae
50 Isochrysis galbana q 50 of Chaetoceros gracilis , three other groups received 70 of the same mixture of microalgae plus 30 carbohydrates
Ž .
commercial potato’s starch , and the other tanks received 70 microalgae and 30 of a Ž
lipid emulsion. The experimental ICES Internationational Council for the Exploration .
of the Sea lipid emulsion was provided by Artemia Reference Center from Belgium and Ž
. corresponded to the EmDHA one whose composition is described in Caers et al. 1999 .
This experiment was run twice, in different years. For the first experiment animals were fed for 72 days at 3 of the dry biomass per day. The second experiment lasted three
months and the diet amounted to 6 of the dry biomass per day. The duration of the experiments was determined according the progress of gonadal ripening; when about
40 of scallops appeared mature in any of the tanks, the experiment was ended to avoid spontaneous spawning which would have made controlled spawning and fertilization
impossible.
Before beginning the conditioning experiment, five spent scallops were sampled to Ž
evaluate gonadal condition using the gonadal index percentage of the total tissue mass .
of the animal that consisted of gonad and histological analysis. Periodically, similar determinations were performed for three animals from each experimental treatment
Ž .
each animal from a different tank to ascertain the course of gonadal recovery. These animals were chosen after visual inspection of all the animals, which were then
separated into three groups according to their degree of apparent maturation. Then, one animal from the largest group in each tank was sampled. The duration of the experi-
ments was determined according the progress of gonadal ripening; when about 40 of scallops appeared mature in any of the tanks, the entire experiment was ended to avoid
spontaneous spawning which would have made controlled spawning and fertilization impossible.
Ž .
On ending the experimental time, animals that looked ripe turgid, orange gonad in each tank were counted, and induced to spawn. The number of scallops that spawned
from each experimental tank was registered. Oocytes obtained from each group were fertilised by the corresponding sperm and the percentage of fertilization was calculated
by counting the number of eggs that were in cleavage stage after two h. The resulting
Ž .
larvae were left in tanks with seawater for 48 h, after which swimming larvae larva D were counted to calculate the percentage survival.
3. Results
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