Galarza, C.M., Fenucci, J.L.
Abstract:
In this work the efficiency of different concentrations of the microalgae Chaetoceros gracilis and its combination with a microencapsulate commercial diet as a feed for protozoeal stages of P. muelleri are analyzed.
Nauplii IV of this species were stocked in 2 1 plastic containers, filled with filtered sea water. Stocking density was 100 nauplii/1. Water quality parameters were: temperature: 21 +/- 2 C; salinity: 33.0 ppt; pH: 7 - 7.5; dissolved oxygen: 6.8 - 7.7 ppm. Water was changed between 50 and 80 % a day, adding in all cases 5 ppm of EDTA. Six treatments were designed and tested in duplicate containers: in the first three, shrimp were fed with 50,000; 100,000 and 150,000 cells/ml of Chaetoceros gracilis while in treatment IV and V concentrations of 100,000 and 30,000 cells/ml of this diatom were supplemented with microencapsulate feed at concentrations between 0.1 - 0.25 and 0.2 - 0.6 ppm respectively; protozoea in treatment VI were fed only microencapsulate ration. Effectiveness of rations were evaluated as function of: time to reach mysis I; growth (total length in microns); survival from protozoea I to mysis I.
The results obtained, at the end of the trial, are shown in the following table:
Algae concentrations (cell/ml):
50,000: 72.3 (% survival); 14 (days to reach Mysis I); 2,655 +/- 17.2 (average length (a))
100,000: 86.3 (% survival); 11 (days to reach Mysis I); 2,729 +/- 12.6 (average length (a))
150,000: 69.7 (% survival); 9 (days to reach Mysis I); 2,857 +/- 13.8 (average length (a))
100,00 + F (b): 65.9 (% survival); 10 (days to reach Mysis I): 2,657 +/- 15.6 (average length (a))
30,000 + F (b): 65.9 ( % survival); 15 (days to reach Mysis I); 2,623 +/- 12.4 (average length (a))
F (b): 7.4 (% survival); 15 (days to reach Mysis I); 2,500 +/- 11.5 (average length (a))
(a) - average length of mysis in microns
(b) F: Commercial feed
Survival from PZ-I to M-I stage ranged between 65.7 and 86.3 %, except for shrimp fed commercial ration (7.4%). No significant differences in mysis' sizes were found among treatments. Days to reach mysis I stage were 9, for shrimp fed algae concentration 150,000 cells/ml, and 14 days for animals to which 50,000 cells/ml were given. Only 7.4 % of shrimp fed commercial diet reached the mysis stage.
Finally, the best algal concentration for larval development of protozoean stages of Pleoticus muelleri ranged from 100,000 to 150,000 cells/ml; on the other hand, commercial ration do not improve larval growth and survival.
(Comision de Investigaciones Cientificas de la Pcia. de Buenos Aires, Argentina)
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