Aspects of the Life Cycle of Chirostoma jordani (Pisces: Atherinopsidae) in A Periurban Lake from Mexico City: An Ecophysiological Assessment

Abstract

Chirostoma jordani is an endemic species of Mexico, whose populations due to different natural and anthropogenic causes, have experienced a notable decline in recent decades, endangering their permanence in their natural habitat, including the Xochimilco canals. Therefore, this study focused on updating the status of the species in Xochimilco through an ecophysiological analysis with a bioenergetic approach, using as a model the elements (P and R) of the general energy balance equation. The measured performance indicators of the species during an annual cycle were: analysis of the structure of size (total length, TL and weight, W), body composition of the tissue: wet weight (WW), dry weight (DW), body water content (WC), nitrogen and energy content, growth rate (GR) = production (P), and metabolic rate (R) in relation to body weight in two contrasting seasons of the year (dry and rainy), as well as assimilation efficiency (P + R). The physicochemical dynamics of the habitat of the species was evaluated in all the sampling months, through eight water quality variables and was correlated with the previously indicated performance measures using discriminant analysis. The composition by sizes indicated that the spawning season and the entry of recruits into the population take place during the dry season (February - May), reaching the highest growth rates in the period March - April: 0.23 mm TL/ day, as well as the highest values in: assimilation (2,457.2 cal/g DW/day), energy expenditure in metabolism and tissue energy enrichment (CI95%: 3,493.6 – 4,762.6 cal/g DW), as opposed to the rainy season of the annual cycle: August – November, which is defined by the greatest environmental heterogeneity with extreme values of pH, total solids and nitrite concentrations that interact as constraints on the performance of the population. It is concluded that the population of C. jordani in the study area is subject to extreme environmental pressures, and the quantitative indicators used are of great value to identify and diagnose the risk status of the species and should be used to delimit future actions in its management and conservation.