Feeding Protocol Modulates the Digestive Process in Senegalese Sole (Solea senegalensis) Juveniles

Understanding the daily digestive function could lead to more efficient feeding practices in the farmed fish species. In this work, the effect of several daily feeding protocols was assessed on the daily expression of the genes related to the circadian system (arntl1, clock, per1, and cry1), appetite (cck), nutrients hydrolysis (try1, ctrb1, pga, atp4a, cel, and amy2a), peptides transport (slc15a1), pH, and activity of key digestive (trypsin, chymotrypsin, amylase, 4C- and 7C-like lipases) and absorptive (alkaline phosphatase) enzymes in the gastrointestinal tract (GIT) of Senegalese sole (Solea senegalensis) juveniles. Some of the tested feeding protocols demonstrated a significant influence on the entrainment of the peripheral oscillator. The synchrony of slc15a1 and some digestive proenzymes with per1 in some of the experimental treatments could underline the role of clock genes in the regulation of these biological functions. Unlike gene expression of the digestive proenzymes wherein feeding protocol occasionally affected the temporal organization, the influence of this factor was determinant on the daily average production and/or circadian pattern of their activities. Daily pH was maintained at approximately neutral levels in all the GIT segments, and no pepsin activity was detected. Fish fed a single diurnal meal showed the lowest activity for all the studied enzymes, except for amylase, suggesting an insufficient utilization of the ingested nutrients. Higher amylase activity in this group, on the other hand, implies the possible activation of alternative compensatory metabolic pathways. Overall, our results pointed to the suitability of higher feeding frequencies, especially during dark hours, for the aquaculture production of this species.

Chromosome anchoring in Senegalese sole (Solea senegalensis) reveals sex-associated markers and genome rearrangements in flatfish

The integration of physical and high-density genetic maps is a very useful approach to achieve chromosome-level genome assemblies. Here, the genome of a male Senegalese sole (Solea senegalensis) was de novo assembled and the contigs were anchored to a high-quality genetic map for chromosome-level scaffolding. Hybrid assembled genome was 609.3 Mb long and contained 3403 contigs with a N50 of 513 kb. The linkage map was constructed using 16,287 informative SNPs derived from ddRAD sequencing in 327 sole individuals from five families. Markers were assigned to 21 linkage groups with an average number of 21.9 markers per megabase. The anchoring of the physical to the genetic map positioned 1563 contigs into 21 pseudo-chromosomes covering 548.6 Mb. Comparison of genetic and physical distances indicated that the average genome-wide recombination rate was 0.23 cM/Mb and the female-to-male ratio 1.49 (female map length: 2,698.4 cM, male: 2,036.6 cM). Genomic recombination landscapes were different between sexes with crossovers mainly concentrated toward the telomeres in males while they were more uniformly distributed in females. A GWAS analysis using seven families identified 30 significant sex-associated SNP markers located in linkage group 18. The follicle-stimulating hormone receptor appeared as the most promising locus associated with sex within a region with very low recombination rates. An incomplete penetrance of sex markers with males as the heterogametic sex was determined. An interspecific comparison with other Pleuronectiformes genomes identified a high sequence similarity between homologous chromosomes, and several chromosomal rearrangements including a lineage-specific Robertsonian fusion in S. senegalensis.