Molecular cytogenetics insights in two pelagic big-game fishes in the Atlantic, the tarpon, Megalops atlanticus (Elopiformes: Megalopidae), and the sailfish, Istiophorus platypterus (Istiophoriformes: Istiophoridae)

Rodrigo Xavier Soares,Gideão Wagner Werneck Félix Da Costa,Luiz Antonio Carlos Bertollo,Clóvis Coutinho Da Motta-Neto,Marcelo De Bello Cioffi,Wagner Franco Molina

doi:10.1590/1982-0224-2021-0007

Rodrigo Xavier Soares, Gideão Wagner Werneck Félix Da Costa + Show 4 more

Open Access

https://doi.org/10.1590/1982-0224-2021-0007

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Abstract

Abstract Some pelagic and usually large sized fishes are preferential targets for sport and commercial fishing. Despite their economic importance, cytogenetic data on their evolutionary processes and management are very deficient, especially due to logistical difficulties. Here, information for two of such charismatic species, the tarpon, Megalops atlanticus (Elopiformes: Megalopidae), and the sailfish, Istiophorus platypterus (Istiophoriformes: Istiophoridae), both with a wide Atlantic distribution, were provided. Cytogenetic data were obtained using conventional methods (Giemsa staining, Ag-NORs technique, and C-banding), base-specific fluorochrome staining and fluorescence in situ hybridization (FISH) with rDNA probes. Megalops atlanticus has 2n = 50 chromosomes, all acrocentric ones (NF = 50), while Istiophorus platypterus has 2n = 48 chromosomes, 2m + 2st + 44a (NF = 52). Megalops atlanticus populations from the South Atlantic and Caribbean share identical karyotypic patterns, likely associated with gene flow between them. In turn, I. platypterus presents karyotype similarities with phylogenetically close groups, such as Carangidae. The chromosomal characteristics of these species highlight their independent evolutionary paths. Additionally, the current data contribute to knowledge of new aspects of pelagic fish fauna and will support further comparative studies with congeneric species, clarifying evolutionary karyotype trends of these fish groups.

Highlights

Pelagic ecosystems represent one of the largest environments on the planet and, in general, little is known about the evolutionary features of its ichthyofauna
In M. atlanticus they are interstitially located in the long arms of the smallest 25th pair, while in I. platypterus they are terminally located in the short arms of the 2nd pair (Fig. 2, highlighted)
These sites are in agreement with the location of the 18S rDNA hybridization signals, being MM+/DAPI- stained, which characterizes them as GC-rich regions (Fig. 2, highlighted)

Summary

Introduction

Pelagic ecosystems represent one of the largest environments on the planet and, in general, little is known about the evolutionary features of its ichthyofauna. Marine pelagic fishes can reach an extensive geographical distribution, a condition that has direct implications for their genetic and cytogenetic patterns (Galetti et al, 2000, 2006; Soares et al, 2013, 2017). A large phylogenetic spectrum of fish groups inhabit the pelagic ecosystems, including representatives of the orders Elopiformes and Istiophoriformes. Elopiformes (9 spp.) is hundreds of times less diverse than other Elopomorpha groups, such as Anguilliformes (995 spp.) (Fricke et al, 2020). Due to their phylogenetically position and evolutionary aspects, the cytogenetic patterns of Elopiformes are one important element that contributes to clarify the karyotype evolution in Teleostei as a whole

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