# Growth and Developmental Processes Alternate During Larval Development of Atlantic Herring

## TL;DR

Atlantic herring larvae experience alternating periods of growth and development, such as muscle and skeleton formation, during their early life stages.

## Contribution

This study identifies two major growth phases in herring larvae and shows how these alternate with developmentally active periods.

## Key findings

- Two major growth periods occur during larval herring development, linked to fin development phases.
- Muscle fiber increases coincide with these growth periods, supported by gene expression data.
- Developmental processes like skeletogenesis occur during periods of reduced growth.

## Abstract

During their development, fish pass through a series of developmental processes advancing, for example, their physiological and locomotive abilities. In particular, many marine fish larvae often hatch at an (semi‐) embryonic developmental stage, and existential processes, such as digestion and respiration, and structures, such as muscle and skeleton, must form and/or change during the larval development. In this study, we analyzed the gene expression of factors associated with myogenesis, skeletogenesis, and growth within the different larval life stages of Atlantic herring. We evaluated these results in relation to length and stage ratio and performed histological analysis of cross‐sections of herring larvae in different stages. Overall, the length per stage ratios showed that there are two major growth periods in larval herring development, the first occurring during the dorsal fin development phase and the second during the transition from caudal fin to pelvic fin development phase. This is consistent with the histological analysis, as an increase in muscle fibers was observed in both phases. The gene expression data also showed that factors responsible for muscle cell lineage determination and fiber development were highest before a period with increased growth. Combining our results with other studies on skeletogenesis, organogenesis, and the development of neural and sensory systems in herring, it becomes evident that other energetically costly developmental processes tend to occur in periods when growth is less prominent. It can therefore be concluded that growth and developmental priority periods alternate during larval development.

During their development, fish pass through a series of developmental processes advancing, for example, their physiological and locomotive abilities. Gene expression analysis combined with histological and morphological analysis of Atlantic herring in different larval life stages showed two major growth periods in larval herring development alternating with periods of increased development, for example, of the skeleton.