Effects of both ecdysone and the acclimation to low temperature, on growth and metabolic rate of juvenile freshwater crayfish Cherax quadricarinatus (Decapoda, Parastacidae)
ABSTRACT. Growth, metabolic rate, and energy reserves of Cherax quadricarinatus (von Martens, 1868) juveniles were evaluated in crayfish acclimated for 16 weeks to either 25°C (temperature near optimum) or 20°C (marginal for the species). Additionally, the modulating effect of ecdsyone on acclimation was studied. After 12 weeks of exposure, weight gain of both experimental groups acclimated to 25°C (control: C25, and ecdysone treated: E25) was significantly higher than that of those groups acclimated to 20°C (C20 and E20). A total compensation in metabolic rate was seen after acclimation from 25°C to 20°C; for both the control group and the group treated with ecdysone. A Q 10 value significantly higher was only observed in the group acclimated to 20°C and treated with ecdysone. A reduction of glycogen reserves in both hepatopancreas and muscle, as well as a lower protein content in muscle, was seen in both groups acclimated to 20°C. Correspondingly, glycemia was always higher in these groups. Increased lipid levels were seen in the hepatopancreas of animals acclimated to 20°C, while a higher lipid level was also observed in muscle at 20°C, but only in ecdysone-treated crayfish. KEYWORDS. Energy reserves, growth, metabolic rate, Q 10 . RESUMEN. Efectos de ecdisona y de la aclimatación a baja temperatura, sobre el crecimiento y la tasa metabólica de juveniles de la langosta de agua dulce Cherax quadricarinatus (Decapoda, Parastacidae). Se evaluaron las reservas energéticas, el crecimiento y la tasa metabólica de langostas juveniles de agua dulce Cherax quadricarinatus (von Martens, 1868), aclimatadas durante 16 semanas tanto a 25°C (temperatura cercana al óptimo) como a 20°C (temperatura marginal para la especie). Adicionalmente, se evaluó el efecto modulador de la ecdisona sobre la aclimatación. Luego de 12 semanas de exposición, la ganancia en peso de ambos grupos experimentales aclimatados a 25°C (control: C25, y tratados con ecdisona: E25) fue significativamente mayor que la de los grupos aclimatados a 20°C (C20 and E20). Se verificó una compensación total en la tasa metabólica, luego de la aclimatación desde 25 a 20°C, tanto para el grupo control como para el tratado con ecdisona. Solamente se observó un valor de Q 10 significativamente mayor en el grupo aclimatado a 20°C y tratado con ecdisona. En ambos grupos aclimatados a 20°C, se determinó un reducción en la reservas de glucógeno, tanto en hepatopancreas como en músculo, así como un menor contenido de proteína en músculo. Correspondiente, la glucemia resultó siempre más elevada en esos grupos, que también mostraron un mayor nivel de lípidos en el hepatopancreas, siendo mayor el nivel de lípidos en músculo sólo para los juveniles aclimatados a 20°C y tratados con ecdisona. PALABRAS-CLAVE. Reservas energéticas, crecimiento, tasa metabólica, Q 10 . Metabolic rate of invertebrates depends on several intrinsic and extrinsic factors. Intrinsic factors include: age, gender, weight, degree of locomotor activity and internal work. Extrinsic factors include: ambient temperature, photoperiod, impact of stressors and food availability. Temperature clearly exerts a major influence on metabolic rate of poikilothermic species. However, most poikilotherms display compensatory mechanisms against temperature change; several species are even capable of full compensation and hold their metabolic rate at the same level they had at a higher temperature after an acclimation period to the new lower temperatur
