Laboratory
analysis of predation by cyclopoid copepods on first-feeding larvae of
cultured Brazilian fishes
C.H. Fregadolli-2003
Aquaculture, 228(1-4): 123-140
Abstract:
Predation by a tropical cyclopoid copepod, Thermocyclops
decipiens, on first-feeding larvae of cultured Brazilian fishes, Piaractus
mesopotamicus and Colossoma macropomum, was studied in the
laboratory. The experiments were designed to quantify the predatory effects
of cyclopoid on larval mortality, fin damage and growth in response to a
broad range of zooplankton that varied with respect to composition, size
structure and abundance. The field-collected zooplankton consisted mainly of
predaceous cyclopoid and cladocerans, an alternative prey to cyclopoid and
principal first food for both fish species. The results indicate that T.
decipiens can adversely affect first-feeding larvae of P.
mesopotamicus and C. macropomum. Dead larvae were found partly or
completely eaten and surviving larvae had parts of the lobe of fins damaged
at the end of the experiments. Only adult and later stage copepodid females
were associated with damage to larvae. Immediate effects of cyclopoid
attacks were evaluated by larval mortality rate and fin damage magnitude of
survivors. Both were found to be positively predator density-dependent and
significantly suppressed by alternative prey presence, especially at high
proportion of cladoceran to cyclopoid. When there was no immediate larval
mortality, cyclopoid presence was related with a reduced larval growth over
the 3.5 initial days of feeding. Larval growth was more negatively affected
by predator density than positively affected by larval food density, a
possible reflection of stress caused by successive cyclopoid attacks. The
results suggest that cyclopoid and larval food densities are the most
important determinants of the degree of damage caused by cyclopoid attack on
fish larvae in the period of first-feeding and have important applied
implications.
(Universidade Federal de São Carlos, Centro de Ciências
Biológicas e da Saúde, Programa de Pós-Graduação em Ecologia e Recursos
Naturais, Via Washington Luiz, Km 235, 13565-905, São Carlos, SP, Brazil,
e-mail: chdolli@uol.com.br)