Abstract
The exposure of adult fish to warm or high temperatures is known to impair reproduction, yet the long-term reproductive impacts for treatments at early life are not well clarified. This study aimed to evaluate the effects of warm temperature (WT) during juvenile stage on gonad maturation, gamete quality, and offspring thermotolerance in rainbow trout. While the comparison of basic reproductive parameters in WT females did not reveal any kind of impairment, many WT males showed an atrophied, undeveloped gonad, or a smaller testis with lower milt volume; sperm quality parameters in WT males and deformity rates in the respective progeny were also highly affected. However, despite of such negative effects, many of the remaining progeny presented better rates of survival and growth when exposed to the same conditions as those of parental fish (WT), suggesting that thermal stress in parr stage males elicited intergenerational thermotolerance after a single generation. The present results support that prolonged warming stress during early life stages can adversely affect key reproductive aspects, but contrastingly increase offspring performance at upper thermal ranges. These findings have implications on the capacity of fish to adapt and to cope with global warming.
Highlights
The exposure of adult fish to warm or high temperatures is known to impair reproduction, yet the long-term reproductive impacts for treatments at early life are not well clarified
The gonadosomatic index in females was lower in warm temperature (WT) compared to control group (CT) (0.0007 ± 0.0003 vs 0.0012; p = 0.002) whereas no difference was found for males (Fig. 2C)
We demonstrated that exposure to warm temperature in male juveniles affects negatively survival, growth, and fecundity, and the motility of spermatozoa and body formation in the respective progeny
Summary
The exposure of adult fish to warm or high temperatures is known to impair reproduction, yet the long-term reproductive impacts for treatments at early life are not well clarified. Research about how temperature acts on the fish germ line, on gametes production or quality, and on progeny fitness might provide important insights for the evaluation of environmental changes (e.g., global warming) on wild populations and extensive a quaculture[14] In this regard, salmonids are an excellent group of fish to evaluate the effects of increasing temperature because they include several cold-water species that are born in freshwater environments and migrate downward to the river mouths until reaching the sea. Some species present variants that spend their entire life cycle in inland waters (landlocked) such as the rainbow trout (Oncorhynchus mykiss) and the Atlantic salmon (Salmo salar) Regardless of these different life cycles, many salmonids have a high likelihood to experience warm temperatures and hypoxic conditions during the juvenile stage[15,16]. In the case of males, impairment of spermatogenesis and reduced milt volume are reported in fish exposed to high temperature[20,21]
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