The amount of cultured live preys (rotifers and Artemia) in the
rearing tanks was computed by filtering 5 L of water and then counting
the individuals under a stereomicroscope (Leica MZ12). Wild planktonic
preys were sampled by filtering 50 L of tank water, and the benthonic
preys by siphon-sucking a fixed area (15 ×10−2 m2
) on the inner surface
of each tank. The filtration was carried out with a 45 µm net mesh, and
organisms preserved in 5% phosphate-buffered (0.1 M, pH 7.2) formalin
solution. The total abundance and the life stages of the major wild taxa
were classified and counted in the laboratory using a stereomicroscope;
adult and larval stages of copepods were identified at specific levels,
unlike nauplii, which were simply considered as a standalone group. The
main live stages of copepod species were identified and sized separately.