Non-uniform metamorphosis underlies different development trajectories in hatchery-reared flathead grey mullet (Mugil cephalus)

The flathead grey mullet ( Mugil cephalus ) is at the focus of an intense domestication effort. However, despite significant advances, aquaculture mullets still based on capture wild fingerlings in estuaries and stocking them into ponds. Such reliance seed limits production since it highly seasonal, unpredictable, hinders genetic improvement programs may negatively affect local fisheries. As captive breeding has been optimized for species, to date, larval rearing remains main challenge hindering commercial captive-bred mullets. Here we set out characterize development under conditions identify key developmental bottlenecks. By analyzing four batches from a hatchery, defined ten distinct stages hatching end metamorphosis macroscopically observable morphological features. Using this atlas study dynamics, found that larvae exhibit biphasic growth profile with 17-fold increase rates onset metamorphosis. Moreover, within batches, size variation almost doubles metamorphosis, suggesting critical step increases by dictating different trajectories early late-metamorphosing larvae. plotting against morphometric parameters, show here age poor predictor due large variations both between batches. We begin threshold ~4.5 mm, however varies greatly even This variance further amplified aforementioned enhanced results non-uniform fry, which complicate weaning procedures. Understanding treating underlying causes delayed are therefore considered important steps full mullet.