The prasinophyte Tetraselmis tetrathele is an important live feed organism for shrimp/prawn hatchery operations because of its high nutritional value and ease of culture. It can replace Brachionus plicatilis and Artemia nauplii as live diet during the protozoeal and mysis feeding stage. This study tried to determine the different optimum culture conditions for T. tetrathele, and to evaluate its application in the hatchery production of different penaeid species. Tetraselmis tetrathele was cultured at combinations of six levels of salinities (10-60 g/kg), nine levels of pH (3-10.5), and two temperatures (25 degrees C and 30 degrees C) in a three factorial combination experiment. Effects of varying concentrations of different organic and inorganic media including the use of vitamins and trace metals were also assessed. The dietary value of I. tetrathele was evaluated by feeding it to different shrimp larvae from protozoea-1 (PZ-l) until postlarva-1 (PL-1).There was no significant difference (P>0.05) in the growth of T. tetrathele at 25 degrees C and 30 degrees C in acidic media; but, there were significant differences (P<0.05) in the range favoring fast growth at 25 degrees C. For the inorganic media test, the optimum concentration for the maximum growth rate of T. tetrathele was at 1 g kg(-1) of Yashima medium without urea (k=0.57). The growth rate for the other media was highly variable with some approximating the optimum. For inorganic nutrients, the optimum concentration for maximum growth was at 4 g/kg of unsterilized 'bio-conversion' medium with 30 mg/l of Clewat-32 (k=0.72). The other growth rates also indicated significant positive rates but were far from the optimum.The combination of T. tetrathele and Chaetoceros gracilis or C. calcitrans could be used as the only diet from protozoea-1 (PZ-I) until postlarva-1 (PL-1) for Metapenaeus ensis, Metapenaeopsis barbata, Trachypenaeus curvirostris, Penaeus indicus, P. merguiensis, P. latisulcatus, and P. japonicus, with high survival rates. However, the larvae of P. semisulcatus, P. monodon and P. chinensis can benefit from a pure phytoplankton diet until the second mysis stage (M-2) only. Beyond this stage, the larvae need bigger zooplankton as live feed.
(Univ. Philippines, Coll. Fisheries, Iloilo, Philippines)
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