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First published online May 24, 2005
Journal of Experimental Biology 208, 2037-2043 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01584

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Olfactory discrimination of female reproductive status by male tilapia (Oreochromis mossambicus)

A. Miranda¹, O. G. Almeida¹, P. C. Hubbard^1,*, E. N. Barata^1,2 and A. V. M. Canário¹

¹ Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
² Departamento de Biologia, Universidade de Évora, Apartado 94, 7002-554 Évora, Portugal

View larger version (12K): [in a new window]   Fig. 1. Comparison of eggs from pre- and post-ovulatory female tilapia. (A) Mean egg mass was significantly higher in pre-ovulatory (Pre; filled bar) than in post-ovulatory females (Post; open bar). Data are shown as means ± S.E.M.; **P<0.01). (B) Frequency distribution of egg diameters from pre-ovulatory (filled bars) and post-ovulatory (open bars) females. Note the presence of larger eggs undergoing maturation in pre-ovulatory females.

View larger version (14K): [in a new window]   Fig. 2. Electro-olfactograms (EOGs) recorded from male tilapia in response to extracts of female water. (A) Typical EOGs recorded in response to pooled extracts of water (diluted 1:100) from pre-ovulatory (shaded horizontal bar, left panel) and post-ovulatory (shaded horizontal bar, right panel) females. A downward deflection of the EOG trace is negative. (B) Semi-logarithmic plot of pooled normalized EOG amplitudes (N=6) to pooled extracts of female water from pre-ovulatory (filled circles) and post-ovulatory (open circles) females at three dilutions. An equivalent dilution to give the same concentration as the original water sample would be 1:2000. ***P<0.001.

View larger version (20K): [in a new window]   Fig. 3. Semi-logarithmic plots of pooled normalized electro-olfactogram (EOG) amplitudes recorded from male tilapia (N=6) in response to pooled urine (A), faeces (B), plasma (C) and bile fluid (D) from pre-ovulatory (filled circles) and post-ovulatory (open circles) females. Comparison of the regression lines revealed significant differences between the elevations (but not the slopes) of the response to urine from pre- and post-ovulatory females and between the elevations (but not the slopes) of the response to faeces from pre- and post-ovulatory females. No differences were found between the responses to plasma (P=0.845) or bile (P=0.923) from pre- and post-ovulatory females. Estimated thresholds of detection are given in the text. *P<0.05; ***P<0.001.

View larger version (11K): [in a new window]   Fig. 4. Urination rates of male tilapia in isolation and in the presence of pre- or post-ovulatory females. Histograms showing the rates of urination of sham-operated (A) and anosmic (B) males in isolation (control; open bars) and in the presence of a pre-ovulatory (black bars) or post-ovulatory (grey bars) female (N=6). Different letters indicate significant differences (P<0.01).

View larger version (11K): [in a new window]   Fig. 5. Effect of anosmia on behaviour of male tilapia in the presence of pre- or post-ovulatory females. Histograms of the proportion of time spent by anosmic (filled bars) and sham-operated (open bars) males in different behavioural categories in the presence of pre-ovulatory (A) and post-ovulatory (B) females. Imm=immobile, Swim=swimming, Court=courtship, Agg=aggression, Other=other types of behaviour (see text for details). Data are shown as means ± S.E.M. (N=6). There are no significant differences between the behaviours of anosmic and sham-operated males.