RESUMO

This study determined the physiological and metabolic responses of cultivated Yellowtail Kingfish (Seriola lalandi) juveniles in accordance with their recent thermal history. The fish were acclimated at 20, 23, 26, 29 and 32 °C for 21 days to determine the final preferred temperature, thermal tolerance and the effect of acclimation temperatures on their oxygen uptake and aerobic scope. The final preferred temperature of juveniles was established at 26 °C. The critical thermal maximum (CTmax) ranged from 34.2 to 36.9 °C, while the critical thermal minimum (CTmin) ranged from 10.9 to 17.3 °C, depending on acclimation temperature. With the CTmax and CTmin values, the thermal window was determined to have an area of 258°C2, which is characteristic of subtropical organisms. Although, the metabolic rate was relatively constant (ranging 390.6-449.8 mg O2 kg-0.8 h-1) between 20 and 26 °C (Q10 = 1.6, 1.0), an increase to 544.8 mg O2 kg-0.8 h-1 at 29 °C (Q10 = 1.9) and decrease of 478.4 mg O2 kg-0.8 h-1 at 32 °C (Q10 = 0.6) were observed. The maximum value obtained for aerobic scope was 310.9 mg O2 kg-0.8 h-1 at 26 °C. These results suggest that the acclimation temperature of 26 °C is an optimum thermal condition for a physiological and metabolic performance of yellowtail kingfish juveniles. On the contrary, the response observed during the evaluation of critical temperatures, oxygen uptake and aerobic scope indicated that yellowtail kingfish in the juvenile state could be vulnerable when it experiences for long periods (e.g., >21 days) temperatures above 29 °C. According to our results, the thermoregulatory behaviour of yellowtail kingfish in the juvenile stages could be one of the most important mechanisms to maintain its optimal physiological performance by actively selecting a stable thermal environment close to 26 °C. In addition, it was determined the limits of the pejus state of juvenile yellowtail kingfish at 29 °C, where an increase of oxygen uptake to maintain the aerobic energy metabolism was observed, this could certainly affect the growth of juveniles in culture systems if they do not return in a thermal range of 23-26 °C. These results can contribute to infer the different effects of acclimation temperature on the growth, thermal tolerance and respiratory capacity of S. lalandi juveniles on aquaculture systems.

Assuntos

RESUMO

Octopus maya endemic to the Yucatan Peninsula, Mexico, is an ectotherm organism particularly temperature-sensitive. Studies in O. maya females show that temperatures above 27°C reduce the number of eggs per spawn, fertilization rate and the viability of embryos. High temperatures also reduce the male reproductive performance and success. However, the molecular mechanisms are still unknown. The transcriptomic profiles of testes from thermally stressed (30°C) and not stressed (24°C) adult male octopuses were compared, before and after mating to understand the molecular bases involved in the low reproductive performance at high temperature. The testis paired-end cDNA libraries were sequenced using the Illumina MiSeq platform. Then, the transcriptome was assembled de novo using Trinity software. A total of 53,214,611 high-quality paired reads were used to reconstruct 85,249 transcripts and 77,661 unigenes with an N50 of 889 bp length. Later, 13,154 transcripts were annotated implementing Blastx searches in the UniProt database. Differential expression analysis revealed 1,881 transcripts with significant difference among treatments. Functional annotation and pathway mapping of differential expressed transcripts revealed significant enrichment for biological processes involved in spermatogenesis, gamete generation, germ cell development, spermatid development and differentiation, response to stress, inflammatory response and apoptosis. Remarkably, the transcripts encoding genes such as ZMYND15, KLHL10, TDRD1, TSSK2 and DNAJB13, which are linked to male infertility in other species, were differentially expressed among the treatments. The expression levels of these key genes, involved in sperm motility and spermatogenesis were validated by quantitative real-time PCR. The results suggest that the reduction in male fertility at high temperature can be related to alterations in spermatozoa development and motility.