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It is well known that in pejerrey water temperature not only affects growth rates but also directs the sexual differentiation process. This fact rise the question of how different the development of pejerrey larvae of the same age is when reared at different temperatures. A description of developmental stages for the embryonic and larval periods of the pejerrey, Odontesthes bonariensis, and the influence of rearing temperature on larval development are presented. Then, larval development was studied at three rearing temperatures, and changes in general morphology, fin morphology, and caudal fin structure have been taken into consideration within the thermal range involved in the temperature sex determination of this species. Fin fold reabsorption, caudal fin formation, and body shape were selected to follow the events leading to the acquisition of the juvenile morphology. The juvenile phenotype was defined when the fin fold was reabsorpted and the caudal fin acquired its definitive homocercal structure. The moment at which the juvenile phenotype was achieved, was evaluated in relation to larval age, size and, shape. The size resulted as the best indicator of development in pejerrey.A temperatura da água não afeta apenas as taxas de crescimento no peixe-rei, mas também direciona o processo de diferenciação sexual. Este fato levanta o questionamento de quão diferente é o desenvolvimento de larvas do peixe-rei da mesma idade quando criadas em temperaturas diferentes. Este trabalho teve como objetivo apresentar uma descrição do de desenvolvimento de embriões e larvas do peixe-rei, Odontesthes bonariensis, e a influência da temperatura de criação no desenvolvimento das larvas. Neste trabalho, o desenvolvimento das larvas foi estudado em três temperaturas diferentes de cultivo. Foram consideradas as alterações ocorridas na morfologia geral, assim como na morfologia e na estrutura da nadadeira caudal dentro da variação termal da temperatura de determinação sexual desta espécie. A taxa de reabsorção da membrana embrionária, a formação da cauda e o formato do corpo foram selecionados para acompanhar os eventos que levam à aquisição da morfologia juvenil. O fenótipo juvenil foi definido quando a nadadeira caudal foi reabsorvida e a cauda adquiriu a estrutura homocerca. O momento no qual o fenótipo juvenil foi atingido, foi avaliado quanto à idade, tamanho e formato da larva, sendo que o tamanho resultou no melhor indicador do desenvolvimento do peixe-rei.

The global expansion of aquaculture is a constant propagule pressure that enables the establishment of exotic species in freshwater and marine environments. Here, we provide the first report on the presence of exotic coho salmon (Oncorhynchus kisutch) at the extreme south of Patagonia, in the island of Tierra del Fuego (TDF). During the last 6 years, 43 juvenile coho salmon were captured along the Beagle Channel, while one adult was captured in fresh water. Scale analysis showed that migration from fresh water as smolt would occur during their first winter of life. Mitochondrial DNA analyses revealed two haplotypes previously reported in North America and a new haplotype not reported before. We developed an environmental DNA assay for detecting coho salmon DNA from fresh water, obtaining positive results in three rivers. Additionally, one of these rivers was monitored monthly for a year, and we detected coho salmon DNA over 7 months, revealing the probable occurrence of coho salmon juveniles in fresh water. These results suggest the potential establishment of self-sustaining populations of coho salmon in TDF.

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Lampreys are jawless fishes belonging to the order Petromyzontiformes. Geotria australis is the sole representative lamprey species of the Geotriidae family and is widely distributed around South America, Australia, New Zealand, and sub-Antarctic Islands. In South America, the presence and distribution of G. australis are well characterized in Western Patagonia, in rivers flowing into the Pacific Ocean. In contrast, there is scarce information about the presence of this species in Eastern Patagonia, in rivers flowing into the Atlantic Ocean. Here, we provide the first report on the distribution of lamprey at the extreme south of Patagonia and suggest the occurrence of a new lamprey species. We developed an environmental DNA (eDNA) method to detect G. australis from water samples and obtained positive results in five basins flowing into the Atlantic Ocean and one river basin flowing into the Beagle Channel. Lampreys were captured from two eDNA-positive basins and used for genetic analysis. An 875 bp-sequence of the cytochrome b mitochondrial gene was obtained, and a phylogenetic analysis was carried out with this sequence and those available in GenBank, revealing Argentinean lamprey reported here, as a sister species of G. australis from Chile, Australia, and New Zealand. Also, the genetic distance values between lamprey reported here and G. australis were consistent with the genetic distances between species of different genera. Our results suggest that the Argentinean lamprey corresponds to a new specific taxon that could represent a new monotypic genus in Geotriidae.

This study evaluated the effect of pejerrey Odontesthes bonariensis (Valenciennes, 1835) broodstock age on gamete and spawning quality and its relationship with sex steroid plasma levels. Sperm was analysed using a computer‐assisted sperm analysis (CASA) developed for pejerrey. Semen samples were taken from all fish from mid age groups (5‐ and 7‐year fish), but it was not possible to obtain stripped semen samples from all fish of younger (3‐year) or older (10‐year) groups. The highest relative sperm weight and sperm concentration were recorded in 5‐ and 7‐year groups respectively, while viability was not different between age groups. It was not possible to identify an effect of age on sperm quality by CASA. Non‐viable spawned eggs were obtained in the 3‐year group and, the relative fecundity and the relative number of fertilized eggs decreased with age in other groups. Fertilization and hatching rates showed the highest values in the 10‐year group. However, the estimated number of hatched larvae was similar in 5‐, 7‐ and 10‐year fish. A clear effect of age on 11 ketotestosterone (11‐KT) and estradiol (E2) levels was identified, with the highest values in the 5‐ and 7‐year groups. These results might be related to the onset of puberty in the 3‐year group and ageing in the 10‐year group. Considering that the estimated number of larvae obtained was similar among age groups, the results of this study suggest that broodstock maintenance cost could be reduced by using mid‐age fish rather than older fish in pejerrey hatcheries.