# Unveiling Embryonic Development of the Threatened Neotropical Fish Prochilodus vimboides (Characiformes: Prochilodontidae)

## TL;DR

This study details the early embryonic and larval development of the endangered Neotropical fish Prochilodus vimboides, providing insights to aid conservation and captive breeding.

## Contribution

The study provides a detailed timeline and characterization of embryonic development stages for the endangered Prochilodus vimboides under captive conditions.

## Key findings

- Hatching of Prochilodus vimboides occurs approximately 22 hours after fertilization.
- Key developmental stages such as gastrula and organogenesis were precisely timed using degree-hour measurements.
- Larvae showed yolk sac absorption without cannibalistic behavior, supporting captive breeding feasibility.

## Abstract

Prochilodus vimboides is a Neotropical freshwater fish native to the Paraíba do Sul and Paraibuna Rivers and is currently classified as endangered. Knowledge of embryonic and early larval development is essential to improve captive breeding programs and support conservation efforts for this species. In this study, broodstock were hormonally induced to reproduce under controlled laboratory conditions, and offspring development was monitored from fertilization to hatching. Shortly after fertilization, fertilized eggs increased in size and underwent rapid cleavage. As development progressed, major embryonic structures such as the head, tail, eyes, musculature, and yolk sac gradually differentiated. Hatching occurred at approximately 22 h after fertilization, followed by progressive yolk sac absorption during the larval phase. In summary, the present work provides a detailed characterization of the early development of P. vimboides, contributing to broader knowledge of this threatened Neotropical species.

Understanding embryonic development is fundamental to improving captive breeding protocols and supporting conservation strategies for threatened fish species. Prochilodus vimboides is a Neotropical freshwater fish for which detailed information on early ontogeny remains scarce. This study aimed to characterize the embryonic and early larval development of P. vimboides under captive conditions. Broodstock were hormonally induced to reproduce, and extrusion occurred between 209 and 230 degree-hours after induction at 21.49 ± 0.15 °C. Embryonic development was monitored at regular intervals after fertilization (AF) using freshly collected eggs examined under a stereomicroscope. The principal developmental stages were identified, namely zygote, cleavage, including morula and blastula, gastrula, organogenesis, and hatching. Fertilized oocytes exhibited marked hydration and formation of a large perivitelline space at 15 min AF. More than 50% of embryos reached the two-blastomere stage by 20 min AF, and cleavage continued until 2 h 14 min AF. The gastrula stage was observed at 3 h 23 min AF, blastopore closure occurred at 11 h 47 min AF, and organogenesis began at 12 h 55 min AF. Complete hatching occurred at 22 h 04 min AF, and larvae subsequently initiated yolk sac absorption without cannibalistic behavior. These findings provide a species-specific developmental framework that supports captive production and conservation efforts for P. vimboides in the Paraíba do Sul River Basin.