No abstract

Photoperiod is considered an important synchronizer of biological activities and endocrine pathways, including growth. As ectotherms, fish have many physiological functions controlled by the photoperiod. However, the combined effects of photoperiod and temperature should be clarified, particularly for tropical fish living near their upper thermal limit, as is the case of Amazonian fish. The central aim of this study was to evaluate the combined effect of photoperiod and temperature on growth and physiological aspects of tambaqui (Colossoma macropomum). Juveniles of tambaqui were distributed in 70 L tank, following a factorial design that included three photoperiods (light 0 h: darkness 24 h; light 12 h: darkness 12 h; and light 18 h: darkness 6 h) associated with three temperatures (26, 29, and 32 • C). They were maintained under these conditions for 2 months. Fish reared in the dark at 29 and 32 • C showed better performance compared to fish reared under extended light conditions at all temperatures. Among physiological responses, it has been observed that blood parameters tend to be disturbed with increasing temperature and that extended light conditions at low temperatures caused similar effects on the analyzed fish, suggesting blood hemoconcentration. Fish under extended light conditions showed an increase in glucose, cortisol, cholesterol, and total proteins, indicating additional physiological disturbances. In conclusion, our study shows that, unlike marine and temperate fish, C. macropomum, a fish species endemic to the Amazon, grows better in warmth dark, showing no significant physiological disturbances, similar to observations described for wild animals of this species. Our results support that changes in fish growth occur in response to environmental conditions. Therefore, fish species from freshwater, estuarine, and marine environments, must be specifically analyzed regarding the combination effects of photoperiod and temperature.

Bentonite is a natural clay that presents characteristics such as good capacity to exchange cations, large specific surface area, large porosity, and possibility to undergo intercalation and/or functionalization. This work reports on bentonite functionalization with organomodified alkoxides. Functionalization afforded hybrid materials displaying desirable properties for adsorption of chromium trivalent ions. Infrared absorption spectroscopy, X-ray powder diffraction, thermal analysis, specific surface area analysis, and adsorption experiments with methylene blue helped to characterize the materials and evaluate their cationic exchange capability. These techniques evidenced functionalization of the Brazilian bentonite. Kinetic and equilibrium experiments on the adsorption of chromium trivalent ions aided determination of the equilibrium time of kinetic adsorption isotherms and revealed whether the functionalized matrices adsorbed chromium trivalent ions. Chromium displayed S1 type adsorption isotherms, which confirmed that adsorption capacity originated from cooperative forces between the adsorbate and the hybrid adsorbents.

The combination of cellulosic materials and clays, such as Laponite, can provide composites with superior optical and mechanical properties compared to pristine cellulose. Synthetic clays can also be used as a host matrix for the immobilization of luminescent complexes, as the incorporated complexes may present enhanced emission quantum efficiency, photo and thermostability compared to the non-immobilized ones. In this way, we, herein, report the preparation of luminescent composites through the incorporation of a Eu(III) complex [Eu3+(tta)n] containing Laponite (Lap) into cellulose nanofibers (CNF). The thermogravimetry results show that the obtained CNF/Lap@[Eu3+(tta)n] films present higher thermal resistance than the CNF film. The Eu3+(tta)n species were found in the composite structure with preserved luminescence characteristics, and no leaching or degradation of the organic ligand was observed with the preparation of the composites.