No abstract

Summary 1.The cost of reproduction due to limiting of the reproductive female's locomotion capability has been suggested many times, but has rarely been directly examined, especially in fishes. Here, the effect of pregnancy on swimming performance in the viviparous Mosquitofish, Gambusia affinis, was studied. 2. Eight females of G. affinis were isolated, each in a separate aquarium, and critical swimming speed (U crit ), body mass (BM) and cross-section area were measured every 5 days from the beginning of the pregnancy until 2-4 days after parturition. 3. Swimming kinematics (tail beat frequency and amplitude) was measured in nonpregnant and pregnant females at different swimming speeds. 4. BM increased during pregnancy from 0·47 ± 0·13 g to 0·72 ± 0·19 g, and the crosssection area also increased during pregnancy from 0·21 ± 0·06 cm 2 to 0·32 ± 0·07 cm 2 . U crit decreased from 25·0 ± 1·3 cm s −1 before pregnancy to 20·1 ± 1·5 cm s −1 just before parturition, and returned to 24·7 ± 1·4 cm s −1 2-4 days after parturition. Interindividual variation was repeatable and reflects real differences among individuals. 5. Swimming kinematics was not affected by pregnancy. 6. The results suggest that reductions in U crit are probably because of aerobic constraints and not necessarily due to hydrodynamic changes resulting from changing in body form or plasticity. Moreover, the reduction in U crit is, potentially, a 'cost of reproduction' owing to decrease in the ability to gain food during pregnancy in G. affinis females.

Specimens of the euryhaline cyprinodontid fish, Aphanius dispar, collected in salt ponds, were acclimated to salinities of <1 (freshwater), 35 (seawater), 70, 105, and 140 ppt for 4 wk before measurement of oxygen consumption, critical swimming speed, and routine activity level. Oxygen consumption was similar in <1, 35, and 70 ppt (0.18+/-0.07, 0.17+/-0.06, and 0.16+/-0.04 mL h(-1) g(-1), respectively [mean+/-SD]) but decreased in 105 and 140 ppt (0. 12+/-0.02 and 0.09+/-0.2 mL h(-1) g(-1), respectively). Critical swimming speed and routine activity levels showed the same trend. These results suggest a general decrease in physiological function of A. dispar at extreme salinities.