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In nature, organisms are exposed to variable environmental conditions that impact their performance and fitness. Despite the ubiquity of environmental variability, substantial knowledge gaps in our understanding of organismal responses to nonconstant thermal regimes remain. In the present study, using zebrafish (Danio rerio) as a model organism, we applied geometric morphometric methods to examine how challenging but ecologically realistic diel thermal fluctuations experienced during different life stages influence adult body shape, size, and condition. Zebrafish were exposed to either thermal fluctuations (22–32°C) or a static optimal temperature (27°C) sharing the same thermal mean during an early period spanning embryonic and larval ontogeny (days 0–30), a later period spanning juvenile and adult ontogeny (days 31–210), or a combination of both. We found that body shape, size, and condition were affected by thermal variability, but these plasticity‐mediated changes were dependent on the timing of ontogenetic exposure. Notably, after experiencing fluctuating temperatures during early ontogeny, females displayed a deeper abdomen while males displayed an elongated caudal peduncle region. Moreover, males displayed beneficial acclimation of body condition under lifelong fluctuating temperature exposure, whereas females did not. The present study, using ecologically realistic thermal regimes, provides insight into the timing of environmental experiences that generate phenotypic variation in zebrafish. [ABSTRACT FROM AUTHOR]

Natural environmental change has produced countless opportunities for species to disperse into and persist in habitats where they previously did not exist. Introduction and stocking programmes have facilitated similar sorts of colonization opportunities across considerably greater geographical scales and often in much shorter periods of time. Even though the mechanism of colonization differs, the result can be the same: evolutionary change in the colonizing population in response to novel selection pressures. As a consequence, some human-mediated fish transfers have unintentionally yielded novel research opportunities to study how phenotypes and genes interact with their environment and affect ecological and evolutionary change. The primary purpose here is to explore how work, directly or indirectly involved with human-mediated transfers, has unintentionally yielded novel research and research opportunities in fish ecology and evolution. Insights have produced new knowledge or altered previously held perceptions on topics such as local adaptation, rate of evolutionary change, phenotypic plasticity, alternative reproductive strategies, population structure and colonization probability. Well-documented stocking programmes, especially in terms of history, numbers and original population sources, can provide highly fertile ground for generating further insights on the ecology and evolution of fishes and of the factors likely to influence the success of conservation-based, restoration programmes. [ABSTRACT FROM AUTHOR]

Individual variability in the mating success of male Atlantic cod Gadus morhua was quantified within an aggregation ( n= 59) breeding undisturbed in a large (684 m3) mesocosm tank. Observational and morphometric data were examined to assess the degree to which this mating variation could be explained by aspects of morphology, condition and spawning behaviour. The number of ventral mounts initiated ( i.e. mating success) was highly variable; most mounts were initiated by a very small percentage of available males. The significant correlate of male mating success was mass of the sound producing musculature, i.e. drumming muscles. Neither body size, condition, pelvic and median fin morphology nor aggression influenced the number of ventral mounts initiated by a male. The present study suggests a possible link between sound production and mating success in Atlantic cod. [ABSTRACT FROM AUTHOR]

Polymorphism at five microsatellite genetic markers (genotyped n = 496) and mark-recapture tagging data (tagged n = 9813) were used to define the population structure of brook charr, Salvelinus fontinalis from the Indian Bay watershed, Newfoundland, Canada. Despite the absence of physical barriers to migration among lakes, both genetic and tagging data suggest that brook charr in each lake represent reproductively isolated populations. Exact tests comparing allele frequencies, θ (global value = 0·063), R st (global value = 0·052), individual assignment tests, and Nei's genetic distance provided congruent estimates of population subdivision in agreement with the tagging data (only 2·2% of recaptures were lake-to-lake). The genetic structure of the brook charr populations corresponded with the geographic structure of the drainage basin on a qualitative level, although linear distance over water was not significantly correlated with the tagging data or the genetic distance measures. The agreement between the tagging and the genetic data suggest that microsatellite markers can be useful tools for defining real biological units. The results also suggest that brook charr exhibit microgeographic population structure at the watershed scale, and that this is the scale at which conservation and management of this salmonid might best be implemented. [ABSTRACT FROM AUTHOR]

The incidence and magnitude of multiple paternity were estimated for a natural, unmanipulated spawning population of Atlantic salmon Salmo salar. Egg nests were surveyed in the autumn and sub-samples were excavated the following spring. Parentage data derived from microsatellite DNA revealed an unexpectedly high level of multiple paternity. Within a single redd, females may mate with as many as 16 different males, including small mature male parr and large anadromous males. Multiple paternity was most pronounced in areas of highest redd density, corresponding with increased abundances of mature male parr. In addition, there was considerable variation in success among males, although this variability did not depend upon the number of males participating in spawning. This work underscores the value of undertaking genetic studies on the mating systems of fishes in unmanipulated, natural environments. [ABSTRACT FROM AUTHOR]