Fertilized eggs from a brown trout Salmo trutta population in northern Spain were incubated in the laboratory at 4, 6, 8, 10, 12, 14, 16 and 18° C. Developmental stage and embryo size were monitored by taking samples at regular intervals. Survival was maximal at 8 and 10° C and decreased at higher and lower temperatures. Despite starting development, no embryo hatched at 16 and 18° C, which suggests an upper thermal limit for development between 14 and 16° C. Time required to reach a given ontogenetic stage decreased with increasing temperature. Embryos incubated at lower temperatures were larger at 50% hatching, and these differences persisted throughout the subsequent embryonic period until the start of exogenous feeding. A comparison with previously published data indicates low interpopulation variability in thermal sensitivity of embryonic development, even in consideration of the great latitudinal range of the studies.

–  Our study assesses swimming capacity (speed and stamina) and possible morphometric determinants of locomotor performance of juvenile brown trout (Salmo trutta L.). We addressed these issues at the individual level to have an approach of the functional significance of intraspecific variation in morphological design. Both swimming speed and endurance time showed significant positive relationships with fish length. Size‐corrected values of speed and endurance time were negatively correlated suggesting a phenotypic trade‐off between burst and prolonged swimming. Size was also highly correlated with all the morphological variables measured. Therefore, we used the residuals of the regressions of those variables on fish length to remove the effect of body size. A principal components analysis (PCA) summarised the 12 morphological variables into two factors, which accounted for 44.3% of the variance. PC1 combined several measures of body depth and width, whereas PC2 represented mainly postanal length relative to abdomen length. Relationships between the scores of the two factors and size‐corrected values of maximum swimming speed and endurance time were weak. PC2 showed a significant positive relationship with endurance time; that is, individuals with longer caudal regions were able to swim against water flow for longer periods of time. Stoutness (PC1) showed a marginally significant negative correlation with endurance time. The lack of stronger relationships could be because of the low morphometric variability among the test individuals, all proceeding from the same population, reared in a common environment, and measured at the same ontogenetic stage.

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Critical swimming speed (U crit ) provides a useful estimate of maximum swimming performance for fish larvae that can be used to assess transport and migratory potential. We measured U crit of red drum Sciaenops ocellatus larvae through its ontogeny and compared the swimming performance of laboratory-reared larvae to that of wild-caught individuals. U crit increased with ontogeny (size), even though variability in U crit at any ontogenetic state was large. U crit for wild-caught larvae increased from 9.7 to 22.2 cm s -1 over the range of 8.3 to 16.3 mm TL and from 1.1 to 20.5 cm s -1 over the range of 3.0 to 19.1 mm TL for reared larvae. The ontogenetic increase in critical swimming speed occurred in 2 phases -an early phase of rapid improvement and a later phase of slower improvement. This sharp change in the trajectory of swimming performance coincided with important changes in ecology, morphology, and hydrodynamics. During the early phase, larvae were pelagic, their growth was highly allometric, especially in the caudal region, and they swam in the inertial hydrodynamic regime. The onset of the later phase coincided with settlement into seagrass beds, isometric growth, and inertial effects on locomotion. Wild larvae generally exhibited greater values of U crit than reared larvae of a comparable size, but the difference was not statistically significant. The results of this comparison imply that research on reared larvae may provide naturalistic results for swimming performance and that hatchery-produced larvae may perform certain behaviours well when released into the wild.KEY WORDS: Scaling · Ontogeny · Swimming performance · Settlement · Hydrodynamics · Wild larvae · Reared larvae Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 384: [221][222][223][224][225][226][227][228][229][230] 2009 important question is whether the behaviour, or specifically swimming performance, of reared larvae is similar to that of wild larvae. From the available data, the answers are mixed. It is generally agreed that behaviours with a learned component, such as anti-predator behaviour, will differ between wild and reared individuals because larvae from the 2 sources have very different experiences (Olla et al. 1998, Brown & Laland 2001). However, some tested behaviours present contradictory results. For example, reared fish may swim faster, slower, or they may have performances equivalent to wild fish, with ontogenetic variations further complicating this picture (von Westernhagen & Rosenthal 1979, Danilowicz 1996, Smith & Fuiman 2004). The same is true for other behaviours. So, when using results from reared individuals, it is desirable to compare the behaviour of these larvae to that of wild fish, especially if the results will be used to make inferences about fish in nature (Leis 2006).Some fishes that breed in coastal marine waters use estuaries as nursery habitat for their late-stage larvae and juveniles. To enter an estuary, larvae may rely on passive transport (J...

The maximum swimming stamina of hatchery reared juvenile brown trout Salmo trutta, swimming against a fixed-velocity water flow of 36·6 cm s 1 (6·97 L s 1 ), was achieved at 16·1 C, and a 90% performance level occurred over a breadth of 7·7 C (12·2-19·9 C). The wide range of temperatures at which swimming performance is close to the maximal capacity could be a consequence of the implications for survival of this function. 2000 The Fisheries Society of the British Isles

Because not all females are equally attractive, and because mating reduces the chances of getting further copulations, males should prefer better-quality mates. In this paper, we use the Trinidadian guppy (Poecilia reticulata) to explore the effects of two non-correlated measures of female quality--size and reproductive status--on male mating decisions. All male guppies employ two alternative mating tactics. We found that large females, particularly those from a high predation site, were the target of most sneaky mating attempts. The response persisted in fish raised under standard conditions over several generations in the laboratory. In addition, non-pregnant females received more courtship displays. We conclude that males can discriminate among females and that they uncouple their mating tactics to track different axes of quality.