Soy protein concentrate effects on gut microbiota structure and digestive physiology of Totoaba macdonaldi.

AIMS: Examine the effect of soy protein concentrate (SPC) on allochthonous microbiota, hindgut integrity, and liver tissue of totoaba (Totoaba macdonaldi). METHODS AND RESULTS: Four diets were prepared: control diet (100% fishmeal) and experimental diets containing partial substitution of fishmeal by SPC (15%, 30% and 45% SPC). After 90 days, samples of the hindgut contents were taken to determine the taxonomic composition of the allochthonous microbiota through sequencing of the V3-V4 region of the 16S rRNA gene. Simultaneously, liver and hindgut samples were collected for examination by histological approaches. The SPC modulated the richness and abundance of the accessory microbiota, of which the main operational taxonomic unit showed an increase corresponding to the Phylum Firmicutes (Bacillales and Lactobacillales). With the increase in SPC, a slight decrease in mucosal fold width, a decrease in goblet cells and a slight distortion of the villi in the hindgut were observed. In the liver, SPC was observed to influence hepatocytes morphology through irregular and enlarged nuclei. CONCLUSION: The study demonstrates that Proteobacteria dominated the allochthonous microbiota of subadult totoaba, regardless of the diet. However, the SPC modulated the accessory bacteria communities and caused slight effects on the liver and gut of fish. SIGNIFICANCES AND IMPACT OF THE STUDY: To our knowledge, this is the first study that analyses the effects of SPC on allochthonous microbiota of subadults T. macdonaldi through new generation techniques such as DNA sequencing for metagenomic analysis.

Effects of recent thermal history on thermal behaviour, thermal tolerance and oxygen uptake of Yellowtail Kingfish (Seriola lalandi) juveniles.

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.

Thermal Physiological Performance and Thermal Metabolic Scope of the Whelk Kelletia kelletii (Forbes, 1850) (Gastropoda: Neptuneidae) Acclimated to Different Temperatures.

nvestigations of thermal limits are crucial to understanding climate change ecology because it illuminates how climate will shape future species distributions. This work determined the preferred temperature, critical threshold limits represented by the Critical Thermal Maximum (CTMax) and (CTMin), thermal window, oxygen consumption rate and thermal metabolic scope of Kelletia kelletii acclimated to 13, 16.0, 19.0 and 22.0 ± 1°C to determine if this species is sensitive to global warming. The preferred temperature (PT) of Kellet's whelk was determined using the acute method. The acclimation temperature significantly affected the thermal preference of the marine snail (P < 0.05) and increased from 13.2 to 24.2°C as the acclimation temperature increased from 13.0 to 22.0°C. The PT was 13.4°C. The acclimation temperature did not significantly affect the CTMax (P > 0.05), obtaining a range of 29.2 to 30.2°C. The CTMin had an interval of 9.2°C, at acclimation temperatures of 13 to 16°C, and increased significantly (P < 0.05) at 12.3°C in the acclimation interval of 19-22°C. The thermal window for the different acclimation temperatures was 163.5°C2. The oxygen consumption rate of the snails increased significantly (P < 0.05) when the acclimation temperature increased from 13.0 to 22.0°C, peaking at 63.6 mg of O2 kg-1 h-1 w.w. in snails maintained at the highest acclimation temperature. The thermal metabolic scope increased significantly (P < 0.05) when the acclimation temperature was 13.0°C, with values of 68.7 mg O2 h-1 kg-1 w.w., then decreased significantly (P < 0.05) to 27.9 mg O2 h-1 kg-1 w.w at 32°C. Therefore, the thermal aerobic scope was highest at the temperatures that K. kelletii preferred. These results may partially explain their pattern of distribution on the Baja California coast.

Transcriptomic Analysis Reveals Insights on Male Infertility in Octopus maya Under Chronic Thermal Stress.

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.