RESUMEN
Understanding the processes shaping population structure and reproductive isolation of marine organisms can improve their management and conservation. Using genomic markers combined with estimation of individual ancestries, assignment tests, spatial ecology, and demographic modeling, we (i) characterized the contemporary population structure, (ii) assessed the influence of space, fishing depth, and sampling years on contemporary distribution, and (iii) reconstructed the speciation history of two cryptic redfish species, Sebastes mentella and S. fasciatus. We genotyped 860 individuals in the Northwest Atlantic Ocean using 24,603 filtered single nucleotide polymorphisms (SNPs). Our results confirmed the clear genetic distinctiveness of the two species and identified three ecotypes within S. mentella and five populations in S. fasciatus. Multivariate analyses highlighted the influence of spatial distribution and depth on the overall genomic variation, while demographic modeling revealed that secondary contact models best explained inter- and intragenomic divergence. These species, ecotypes, and populations can be considered as a rare and wide continuum of genomic divergence in the marine environment. This acquired knowledge pertaining to the evolutionary processes driving population divergence and reproductive isolation will help optimizing the assessment of demographic units and possibly to refine fishery management units.
RESUMEN
The goal of this study was to determine rearing conditions that would improve the survival of broodstock of winter flounder Pleuronectes americanus. We hypothesized that keeping wild winter flounder in iso-osmotic water would reduce the energy costs related to osmoregulation; the resulting energy gain could then be used for growth or immune responses. Eighty fish were randomly separated into four tanks, two containing seawater (SW; 28.7 ± 0.9 (mean ± SD)) and two containing brackish water (BW; 14.7 ± 1.7). Fish were sampled after 2 and 5 months of captivity for evaluation of their condition and stress status. Between the second and fifth months, the condition index increased significantly in both salinity groups, whereas body water content decreased. No salinity effect in terms of growth, condition, or energy reserves was found. However, the fish in BW showed much lower mortality. We found that the fish in SW had higher levels of the physiological indicators of stress than those in BW, which could have increased the risk of opportunistic infections in the former. Also, thrombocytes were absent in the SW fish after 2 months of captivity, which may have contributed to some mortalities. The lower resistance of certain opportunistic pathogens to BW is another possible explanation as to why fish in BW had lower occurrences of infectious diseases.
RESUMEN
The goal of this study was to determine rearing conditions that would improve the survival of broodstock of winter flounder Pleuronectes americanus. We hypothesized that keeping wild winter flounder in iso-osmotic water would reduce the energy costs related to osmoregulation; the resulting energy gain could then be used for growth or immune responses. Eighty fish were randomly separated into four tanks, two containing seawater (SW; 28.7 ± 0.9 (mean ± SD)) and two containing brackish water (BW; 14.7 ± 1.7). Fish were sampled after 2 and 5 months of captivity for evaluation of their condition and stress status. Between the second and fifth months, the condition index increased significantly in both salinity groups, whereas body water content decreased. No salinity effect in terms of growth, condition, or energy reserves was found. However, the fish in BW showed much lower mortality. We found that the fish in SW had higher levels of the physiological indicators of stress than those in BW, which could have increased the risk of opportunistic infections in the former. Also, thrombocytes were absent in the SW fish after 2 months of captivity, which may have contributed to some mortalities. The lower resistance of certain opportunistic pathogens to BW is another possible explanation as to why fish in BW had lower occurrences of infectious diseases.
