Early development of the Neotropical fish known as long sardine Triportheus auritus (Valenciennes 1850) (Characiformes, Triportheidae)

Abstract

Larvae and juveniles of long sardine, Triportheus auritus, from the lower Amazon river was described, evaluating ontogenetic changes in their external mor­phology, pigmentation, fin development, morphometry, and meristics. A total of 93 individuals, 83 larvae and 10 juveniles were analyzed, they were captured monthly between 2014 and 2019 in the Amazon river channel and in macrophytes aquatic stands in the alluvial plains located in the lower Amazon River. From each specimen, morphometric and meristic data were measured and then the growth pattern between morphometric variables was analyzed. The larvae have an elongated body in a fusiform shape, superior mouth, simple nostril, pigmented spherical eyes and long intestine, surpassing the median region of the body. Initial pigmentation is scarce, but intensifies through development forming a pattern composed of three longitudinal bands concentrated in the ventral, cephalo‐dorsal and lateral line regions. There are also pigments in the mandible, surrounding the mouth, under the swim bladder, intestine and fins. The sequence of complete fin formation is: caudal, anal, dorsal, pectoral and pelvic. The total number of myomeres ranged from 45 to 48 (25–29 preanal and 17–22 postanal). Morphometric relationships indicated differential growth for measurable morphometric parameters, with abrupt growth of snout length, head length and body height in the transition from flexion to postflexion stages. The pre‐dorsal distance showed a decrease in the growth rate at the threshold from the larval to the juvenile period. The pre‐pectoral and pre‐anal distances showed negative allometric growth. In conclusion, the combination of body shape pigmentation pattern and, the formation sequence of fins allow the identification of the genus and coupled with the number of myomeres, morphometric relationships, and ray numbers of the anal fin ensure the differentiation of T. auritus from the other congeneric species. The metamorphosis occurred mainly at the end of the larval period and it is related to changes in the physiological and ecomorphological characteristics of the species.

Early development ofProchilodus nigricansSpix & Agassiz 1829 (Characiformes: Prochilodontidae) in captivity

“…The opening and functioning of the mouth and anus, together with the pigmentation of the eyes are events that occur simultaneously during the preflexion stage and are linked to the beginning of exogenous feeding of larvae (boiled egg yolk, diluted in water; Cajado et al, 2021; Oliveira et al, 2021; Silva et al, 2021), therefore, P. nigricans larvae were able to receive exogenous feeding from 3 days posthatching and presented a feeding transition period between three and 4 days posthatching. This change from endogenous to exogenous feeding is considered critical for larval survival, being a crucial moment for larviculture success (Abdo et al, 2015), since feeding in the first days of life is one of the main obstacles in the production of fingerlings (Silva et al, 2013).…”

“…The myomeres correspond to the number of vertebrae (all segments of the spine, including the urostile and incorporated the Weber apparatus equivalent to the fusion of four vertebrae) plus one (Snyder, 1979). Thus, the total or partial number of myomeres is considered an important character for the identification of fish larvae (Cajado et al, 2021; Oliveira et al, 2021; Santos et al, 2020; Silva et al, 2021).…”

“…Thus, the total or partial number of myomeres is considered an important character for the identification of fish larvae (Cajado et al, 2021;Oliveira et al, 2021;Santos et al, 2020;Silva et al, 2021).…”

“…After hatching, the individuals were categorized according to the flexion of the final section of the notochord and the development sequence of the fins and their supporting elements, in (I) larval period comprising four stages: (a) yolk sac, (b) preflexion, (c) flexion and (d) postflexion; and (II) juvenile period (Ahlstrom et al, 1976; modified by Nakatani et al, 2001). These classifications are widely adopted in several morphological characterization studies of the early stages of life of freshwater fish (Cajado et al, 2021; Lima et al, 2021; Oliveira et al, 2020; Oliveira et al, 2021; Santos et al, 2020; Silva et al, 2021).…”

“…It is emphasized that although the Amazon region has the greatest fish biodiversity in the world, there are still few studies that address the description of the early ontogeny of fish species (Zacardi et al, 2020). However, knowledge of larval phases is pivotal to assist in the management and conservation of tropical fishery stocks (Cajado et al, 2021; Oliveira et al, 2021; Silva et al, 2021).…”