Metabolic rate and hypoxia tolerance in Girardinichthys multiradiatus (Pisces: Goodeidae), an endemic fish at high altitude in tropical Mexico

Artículo científico JCR Q1The darkedged splitfin (Amarillo fish), Girardinichthys multiradiatus is a vulnerable endemic fish species inhabiting central Mexico's high altitude Upper Lerma Basin, where aquatic hypoxia is exacerbated by low barometric pressures (lower PO2s), large aquatic oxygen changes, poor aquatic systems management and urban, agricultural and industrial pollution. The respiratory physiology of G. multiradiatus under such challenging conditions is unknown - therefore the main goal of the present study was to determine metabolic rates and hypoxia tolerance to elucidate possible physiological adaptations allowing this fish to survive high altitude and increasingly eutrophic conditions. Fish came from two artificial reservoirs – San Elías and Ex Hacienda - considered refuges for this species. Both reservoirs showed high dial PO2 variation, with hypoxic conditions before midday and after 20:00 h, ~4 h of normoxia (15 kPa) from 16:00–20:00, and ~4 h of hyperoxia (16–33 kPa) from 12:00–16:00. Standard metabolic rate at 20 ± 0.5 °C of larvae from Ex Hacienda was significantly higher than those from San Elías, but these differences disappeared in juveniles and adults. Metabolic rate at 20 ± 0.5 °C for adults was 9.8 ± 0.1 SEM μmol O2/g/h. The metabolic scaling exponent for adults was 0.58 for San Elías fish and 0.83 for Ex Hacienda fish, indicating possible ecological effects on this variable. Post-larval fish in Ex Hacienda and all stages in San Elias site showed considerable hypoxia tolerance, with PCrit mean values ranging from 1.9–3.1 kPa, lower than those of many tropical fish at comparable temperatures. Collectively, these data indicate that G. multiradiatus is well adapted for the hypoxia associated with their high-altitude habitat.CONACyT PRODEP-SEP UAEMé

Threatened fishes of the world: Menidia riojai Solórzano and López 1965 (Atheriniformes: Atherinopsidae)

Menidia riojai is endemic of the Lerma River headwaters considered critically endangered because its populations have been severely fragmente

Habitat complexity modulates phenotype expression through developmental plasticity in the threespine stickleback

The expression of alternative phenotypes within a single species is often considered to be the result of ontogenetic processes and specifically phenotypic plasticity responses to exposure to different environmental conditions. In fish, which have been widely used to test such questions, exposure to different diets is the most frequently described initiator of plastic responses. The effect of physical characteristics of the habitat on fish morphology has not been fully explored. In the present study, a clear effect of habitat complexity on fish shape was found. Threespine sticklebacks were exposed to two different habitat treatments, simple and complex, over a 17-week period. The exposure to the habitats resulted in the expression of very significant differences in body and head morphologies and spine position, showing that the physical environment can modulate the expression of traits through phenotypic plasticity during ontogen