February 15-18, 2009 Washington State Convention Center Seattle ...

2
PHOTOPERIOD, AGGRESSIVENESS AND ANDROGENS IN CICHLID FISH Tilapia rendalli
Thaís B. Carvalho*, Eliane Gonçalves-de-Freitas and Rui F. Oliveira
UNESP, Universidade Estadual Paulista
IBILCE, São José do Rio Preto, Brasil
thaisbillalba@gmail.com
Photoperiodic manipulation is emerging as an
acceptable approach of practical application for
increasing growth and reproduction in fish farming.
However, light/dark cycles also can increase
aggressive behavior and androgen levels in fish.
This high aggressiveness is harmful in aquaculture
systems, because it can increases wounds and
mortality of fish.
We tested the effect of photoperiod in aggressive
behavior and the plasma androgen levels (testosterone
and 11-ketotestosterone) in adult males of Tilapia
rendalli. We compared two photoperiods: longday
(16L:08D) and short-day (08L:16D).
Animals were grouped for 20 days in each photoperiod.
After that, animals were separated in two
conditions. Condition I: animals were isolated for 4
days and the basal androgen levels was determined
(long-day: n=14; short-day: n=9); Condition II:
animals were isolated for 3 days and in 4 th day they
were submited to territorial intrusion for 1 hour.
The androgen levels in social challenge was given
(long-day: n=12; short-day: n=10).
The aggressive behavior of winner, loser and pair
were stimulated for long-day (Figure 1). The testosterone
and 11-ketotestosterone levels were similar
between two photoperiods. The androgens levels
were not correlated with aggressive interactions.
Thus, photoperiod interfere in social interactions
in T. rendalli, but this result can not be modulated
by androgens. Moreover, the effect of light phase
in aggressiveness shows that artificial photoperiod
manipulations in fish farming must be made with
caution, because light can modify fish behavior.