Brycon orbignyanus, (Valenciennes, 1850) (Valenciennes, 1850)

Bianchini, Bárbara Correa, Quirino, Patricia Postingel, Cristan, Marina de Oliveira, Delgado, Maria Luiza Ribeiro, Gomes-Silva, Luciane, Benevente, Cristiane Fernanda, Grigoli-Olivio, Maiara Luzia, Ninhaus-Silveira, Alexandre & Veríssimo-Silveira, Rosicleire, 2024, Dispersion of hooks on the anal fins of primary and secondary males in Brycon orbignyanus (Characiformes: Bryconidae): a secondary sexual trait for breeder selection, Neotropical Ichthyology (e 230123) 22 (1), pp. 1-15 : 5-8

publication ID

https://doi.org/10.1590/1982-0224-2023-0123

DOI

https://doi.org/10.5281/zenodo.15491949

persistent identifier

https://treatment.plazi.org/id/03B76E74-7A31-FFDF-FE30-FD6C6DF3FB05

treatment provided by

Felipe

scientific name

Brycon orbignyanus
status

 

RESULTS View in CoL

Anal fin and hook morphology. The anal fins can be divided into cranial, medial and caudal regions and are 6.4 ± 3.1 cm long and possess 25 ± 3 rays ( Figs. 1A, B, D View FIGURE 1 ). A first soft ray of 0.73 ± 0.4 cm in height develops in the cranial region, while the second ray that is the first hard ray is 1.5 ± 0.3 cm in height. The remaining rays possess a mean height of 0.8 ± 0.2 cm ( Figs. 1B, D View FIGURE 1 ).

The anal fin of B. orbignyanus possesses dark red rays and black interradial membranes ( Figs. 1A–D View FIGURE 1 , 2A View FIGURE 2 ). Each ray is formed by segments joined by small joints that may or may not contain hooks ( Figs. 1C View FIGURE 1 , 2A, B View FIGURE 2 ). All rays are covered by an extension of the inter-radial membranes ( Fig. 1C View FIGURE 1 ). Each ray undergoes an initial bifurcation, and as it approaches the final portion, there is a new terminal bifurcation ( Figs. 1C View FIGURE 1 , 2A View FIGURE 2 ).

In non-breeding males, the ray segments were smooth and exhibited no traces of hooks development ( Figs. 2C, E View FIGURE 2 , 3A–C View FIGURE 3 ). However, these animals may undergo the formation of a callosity in the region of articulation between one segment and another ( Figs. 3B, C View FIGURE 3 ), thus giving the false impression that the animal possesses hooks when, in fact, there are none. Calluses are perceived as sporadic elevations and differ from hooks in that there is no sensation of roughness to the touch.

With the naked eye, the hooks can be observed as small elevations along the rays, and they are best observed in the central region of the fin, as the hooks rays decrease in quantity as they approach the caudal region of the animal ( Fig. 2B View FIGURE 2 ). Additionally, the hooks were located from the medial portion towards the terminal portion of the rays, and reached the terminal bifurcations, and they were absent in the initial portion located closer to the stomach of the animal ( Figs. 2B View FIGURE 2 , 4A, B View FIGURE 4 ). Therefore, the sensation of roughness when touching the fins is intense in these regions.

Furthermore, the hooks were located from the medial portion towards the terminal portion of the rays, and reached the terminal bifurcations, and they were absent in the region located closest to the stomach of the animal ( Figs. 2B View FIGURE 2 , 4A, B View FIGURE 4 ). Hooks always emerge in the central region of the ray segment, and therefore, they can be felt from the first signs of growth ( Fig. 4C View FIGURE 4 ). As they develop, these hooks are characterised by small projections that exhibit the shape of keels with a wide cylindrical base and a thin terminal portion that is similar to a hook-shaped tip facing the stomach of the animal ( Figs. 2D–F View FIGURE 2 , 4D, E View FIGURE 4 ). They are arranged from the second to the sixteenth ray and contain only one hook per segment ( Figs. 4D, E View FIGURE 4 ), even after bifurcation. As the rays are cylindrical and each segment possesses only one hook, the hook will only be observed or felt on one side of the fin. Thus, the left or right side of the fins will present or feel differently ( Fig. 4B View FIGURE 4 ).

Relationship between testicular development and the presence of hooks on the anal fin. According to the classification of the phases of the reproductive cycle proposed by Brown-Peterson et al. (2011), the analysed specimens of B. orbignyanus were classified as Immature ( Figs. 5A, B View FIGURE 5 ), Regressing ( Fig. 5C View FIGURE 5 ), Regenerating ( Fig. 5D View FIGURE 5 ), and Spawning Capable ( Figs. 5E, F View FIGURE 5 ) ( Tab. 1 View TABLE 1 ). Except for specimens in Regenerating, in all other stages of the reproductive cycle in B. orbignyanus males with hooks were observed; however, specimens that were Spawning Capable exhibited a greater number of rays that developed hooks ( Tab. 1 View TABLE 1 ). Two individuals that were considered intersex (Immature) ( Fig. 5B View FIGURE 5 ; Tab. 1 View TABLE 1 ) and two secondary males (Spawning Capable) ( Fig. 5F View FIGURE 5 ) were identified ( Fig. 5F View FIGURE 5 ). Both categories (intersex and secondary male) showed the same hooks growth pattern as the other males ( Tab. 1 View TABLE 1 ).

There was a positive correlation (p = 0.0001; R 2 = 0.78) between the phases of testes maturation and the number of rays with hooks in primary and secondary males in Brycon orbignyanus ( Fig. 6 View FIGURE 6 ). Thus, animals that possess more than six rays with the development of hooks are all considered Spawning Capable ( Fig. 6 View FIGURE 6 ). There was a weak correlation between length and rays with hooks (p = 0.001, R² = 0.40) ( Fig. 7 View FIGURE 7 ).

Kingdom

Animalia

Phylum

Chordata

Order

Characiformes

Family

Bryconidae

Genus

Brycon

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