A comparative morphological investigation of otoliths of six parrotfish species (Scaridae) from the Solomon Islands

De Novo Genome Assembly of the Whitespot Parrotfish (Scarus forsteni): A Valuable Scaridae Genomic Resource

Scarus forsteni, a whitespot parrotfish from the Scaridae family, is a herbivorous fish inhabiting coral reef ecosystems. The deterioration of coral reefs has highly affected the habitats of the parrotfish. The decline in genetic diversity of parrotfish emphasizes the critical importance of conserving their genetic variability to ensure the resilience and sustainability of marine ecosystems for future generations. In this study, a genome of S. forsteni was assembled de novo through using Illumina and Nanopore sequencing. The 1.71-Gb genome of S. forsteni, was assembled into 544 contigs (assembly level: contig). It exhibited an N50 length of 17.97 Mb and a GC content percentage of 39.32%. Our BUSCO analysis revealed that the complete protein of the S. forsteni genome had 98.10% integrity. Combined with structure annotation data, 34,140 (74.81%) genes were functionally annotated out of 45,638 predicted protein-coding genes. Upon comparing the genome size and TE content of teleost fishes, a roughly linear relationship was observed between these two parameters. However, TE content is not a decisive factor in determining the genome size of S. forsteni. Population history analysis results indicate that S. forsteni experienced two major population expansions, both of which occurred before the last interglacial period. In addition, through a comparative genomic analysis of the evolutionary relationship of other species, it was found that S. forsteni had the closest relationship with Cheilinus undulatus, another member of the Labridae family. Our expansion and contraction analysis of the gene family showed that the expansion genes were mainly associated with immune diseases, organismal systems, and cellular processes. At the same time, cell transcription and translation, sex hormone regulation, and other related pathways were also more prominent in the positive selection genes. The genomic sequence of S. forsteni offers valuable resources for future investigations on the conservation, evolution, and behavior of fish species.

Scanning electron microscopy and morphological analysis reveal differences in the otolith morphology of three species of the family Lethrinidae (Teleostei: Perciformes) from Yemen

Otoliths, or ear-stones, are calcareous components in the static-acoustic organs of teleost fishes with a characteristic morphology. As such, they are widely used in fisheries because of the information stored in them concerning, for example, environment, age, and so forth. Otoliths of three lethrinid species Lethrinus borbonicus (Valenciennes, 1830), L. lentjan (Lacepède, 1802), and L. mahsena (Forsskål, 1775) were collected from fish caught along the Red Sea coast of Yemen. Images taken with a scanning electron microscope were used to determine their characteristics. Twenty-two characters were defined to describe the shapes of the otoliths. Eleven measurements of distance between selected features were used for a linear regression and multivariate analysis to characterize the species by their otoliths. The results illustrate ontogenetic changes for different age groups based on the recorded shapes. All three species show a linear relationship between the total length and the morphometric measurements. A linear discriminant analysis shows marked differences between the otoliths of the three species and emphasizes the importance of the measured variables. Otoliths of L. lentjan and L. borbinicus are more similar to each other and differ from those of L. mahsena. A comparison with previously published otoliths of the species studied from other areas confirms an intraspecific uniformity across larger geographic distances, making the characters useful for diagnostic purposes.