Simple Summary The meagre is a fish species of recent interest in aquaculture, because of its fast growth and flesh quality. Nevertheless, it hasn't been studied enough, and feed producers do not have enough information about the nutrient requirements to optimize the feed diets of the meagre. This study measures the growth response of this fish to several amounts of food and gives information about the proportion of protein and energy that should be included in its diet, as well as the recommended amount of food to optimize its growth. The meagre is a carnivorous species and might be a suitable candidate species for the diversification of aquaculture in the Mediterranean region. This is based on its high growth and flesh quality. Nevertheless, there is little information available about its growth rates and nutrient requirements. The objective of this study was to determine the protein and energy requirements of juvenile meagre (Argyrosomus regius). Two trials for different weights of 53 and 188 g were conducted with rations from starvation to apparent satiation with the scope of studying its nutritional needs. In the first trial, the initial mean body weight of the fish was 53 g, and they were fed at feeding rates, measured as a percentage of the body weight, of 0, 0.75, 1.5, 2.5, 3.5, and 4.5%, with two replicates per treatment. In a second trial, another group with approximately 188 g of initial body weight was fed at feeding rates of 0, 0.5, 1.5, and 2.5%, with two replicates per treatment. The optimum thermal growth coefficient was obtained with a feed intake of 2.2% day(-1) in trial A and 1.73% day(-1) in trial B. The digestible protein (DP) intake for maintenance was determined as 0.57 g kg(-0.7) day(-1), the DP intake for maximum growth was 6.0 g kg(-0.7) day(-1), and the point for maximum efficiency in protein retention was 1.8 g kg(-0.7) day(-1). The requirement for digestible energy (DE) intake for maintenance was recorded at 25.4 kJ kg(-0.82) day(-1), the DE intake to maximize growth was 365 kJ kg(-0.82) day(-1), and the point for maximum efficiency in energy retention occurs with a digestible energy intake of 93 kJ kg(-0.82) day(-1). The requirements and retention efficiency of protein and energy in Argyrosomus regius tend to be within the range other fish species. The maintenance needs are in agreement with species with low voluntary activity and growth requirements in agreement with fast-growth species.