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In this study, the complete mitochondrial genomes of the Mexican golden trout, Oncorhynchus chrysogaster, and Nelson's trout, O. mykiss nelsoni, were assembled and characterized. The mitogenomes were 16,655 bp and 16,661 bp long, respectively, and were composed of 13 protein-coding genes (PCGs), two ribosomal RNA genes, and 22 transfer RNA genes (all with typical 'cloverleaf' secondary structures). The length of the D-loop regions was among the longest found in Salmonids, and mitochondrial synteny in both species was identical to that reported in other Salmonids. Selective pressure analysis in the PCGs indicated that purifying selection, mainly among cox and nd genes families, likely generated the main differences between the two studied species. Nine tRNA genes showed slight differences relative to other O. mykiss subspecies, which were identical between the two study taxa. The origin of the light-strand replication has a loop that was especially large in O. mykiss nelsoni. Phylogenetic analysis indicated that O. chrysogaster and O. mykiss nelsoni are sister species, contrary to the expectation that O. chrysogaster would cluster with O. gilae. As previous studies have suggested, O. chrysogaster and O. mykiss nelsoni share common ancestry with North American trout species. [ABSTRACT FROM AUTHOR]

“Octopus” rubescens Berry, 1953 is an octopus of temperate waters of the western coast of North America. This paper presents the first record of “O.” rubescens from the tropical Mexican Pacific. Twelve octopuses were studied; 10 were collected in tide pools from five localities and two mature males were caught by fishermen in Oaxaca. We used morphometric characters and anatomical features of the digestive tract to identify the species. The five localities along the Mexican Pacific coast provide solid evidence that populations of this species have become established in tropical waters. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Rickettsiales-like organism from Crassostrea corteziensis is a commensal endosymbiont. • The prevalence and intensity of the Rickettsiales-like organism is low. • 16S rRNA amplicon sequencing shows the presence of intracellular parasite OTUs. Fastidious endosymbiotic Rickettsiales-like organisms (RLOs) have been observed in the digestive diverticula of the cultured pleasure oyster (Crassostrea corteziensis) from Nayarit, Mexico since 2007. In a few mollusk species, these bacteria have been associated with mortality events and production losses. The type of relationship between the RLOs and the pleasure oyster is largely unknown and further investigations are needed to determine if these bacteria warrant management concern in C. corteziensis. In this study, the morphological characteristics of the RLOs were studied by histology and SEM, and the taxonomic affiliations of the bacteria were evaluated by 16S rRNA amplicon sequencing. In addition, the prevalence and intensity of the RLOs was recorded from 2007 to 2017 by histology. The RLOs were observed inside circular basophilic cytoplasmic membrane bound vacuoles (MBVs) that had an average length and width of 15.70 ± 15.24 µm and 15.42 ± 14.95 µm respectively. Apart from cellular hypertrophy, no tissue alterations were observed in the areas adjacent to the RLOs. Individual bacteria within the MBVs were coccoid in shape with an average length of 0.65 ± 0.12 µm and an average width of 0.38 ± 0.09 µm. The bacterial microbiota of a selected number of samples (one sample without RLOs and two samples with RLOs) showed the presence of intracellular parasite OTUs corresponding to the families Rickettsiaceae and Anaplasmataceae, suggesting that the RLOs from the pleasure oyster is associated with the order Rickettsiales. A mean prevalence of 5 % was observed throughout the study period and the majority of the organisms (89 %) presented low intensity of Grade 1 (30–61 RLOs) of the MBVs. A higher prevalence of the RLOs was observed during warmer months. The lack of tissue alterations, the low prevalence and the low intensity of the MBVs suggest that the RLOs from C. corteziensis is a commensal endosymbiont that presents little risk for oyster production in Nayarit, México. However, regular monitoring is needed to detect if any variation in this relationship occurs, mainly in a scenario where extreme environmental fluctuations may occur. [ABSTRACT FROM AUTHOR]