Survival, Growth, and Development in the Early Stages of the Tropical Gar Atractosteus tropicus: Developmental Critical Windows and the Influence of Temperature, Salinity, and Oxygen Availability

Abstract

Alterations in fish developmental trajectories occur in response to genetic and environmental changes, especially during sensitive periods of development (critical windows). Embryos and larvae of Atractosteus tropicus were used as a model to study fish survival, growth, and development as a function of temperature (28 °C control, 33 °C, and 36 °C), salinity (0.0 ppt control, 4.0 ppt, and 6.0 ppt), and air saturation (control ~95% air saturation, hypoxia ~30% air saturation, and hyperoxia ~117% air saturation) during three developmental periods: (1) fertilization to hatch, (2) day 1 to day 6 post hatch (dph), and (3) 7 to 12 dph. Elevated temperature, hypoxia, and hyperoxia decreased survival during incubation, and salinity at 2 and 3 dph. Growth increased in embryos incubated at elevated temperature, at higher salinity, and in hyperoxia but decreased in hypoxia. Changes in development occurred as alterations in the timing of hatching, yolk depletion, acceptance of exogenous feeding, free swimming, and snout shape change, especially at high temperature and hypoxia. Our results suggest identifiable critical windows of development in the early ontogeny of A. tropicus and contribute to the knowledge of fish larval ecology and the interactions of individuals × stressors × time of exposure.

Larval Development in Tropical Gar (Atractosteus tropicus) Is Dependent on the Embryonic Thermal Regime: Ecological Implications under a Climate Change Context

“…Additionally, increased temperature, from 15 to 21 • C (∆6 • C), during embryonic development until hatching in Senegalese sole (Solea senegalensis) leads to an increased incidence of skeletal deformities [15]. Therefore, these results are in line with the reported high resistance of A. tropicus larvae to suboptimal rearing conditions with low requirements for water quality (regarding pH, dissolved oxygen, and pollutants, and with high ammonia tolerance) [24,[45][46][47]. Nevertheless, thermal variation during embryonic development was shown to induce sublethal effects in fish growth, skeletal development, and body morphology.…”

“…In the last decade, greater interest and efforts to increase aquaculture production of tropical gar have been placed due to the reduced capture of this species in the natural environments [28,29]. These efforts have been translated in a broader knowledge on the optimal rearing conditions and husbandry practices [23,24,[38][39][40][41][42]. The optimal rearing temperature is 26-28 • C (Álvarez-González et al, unpublished results); thus, an alteration of just 4 • C seemed to be a quite realistic approach to explore the effects of a heat wave, considering that broader thermal alterations were registered in freshwater bodies [43].…”

“…Lepisosteids are an infraclass of Actinopterygii lacking the extra whole genome duplication of Teleosts, and a key group to understand vertebrate's evolution [22]. Moreover, Lepisosteid larvae are suitable piscine models to study the early life stages of fishes due to their rapid embryonic and larval development [23,24]. In particular, the tropical gar (Atractosteus tropicus), one of the seven extant Lepisosteids, is found in freshwater environments such as rivers, streams, lagoons, and swamps with abundant vegetation from southeast Mexico to Costa Rica [25].…”