In general, marine fish species have a very short period (a “quality window” of few hours) when ovulated eggs are of outstanding quality and when fertilization results in high quality embryos and juveniles. Environmental conditions and broodstock tank construction should therefore be conducive to the occurrence of natural spawning, ensuring the collection of embryos of the highest possible quality. Under the correct environmental conditions, the most important of these being temperature and photoperiod regimes, combined with the proper physical surroundings, courtship and mating will take place in populations of captive broodstock. In addition to increasing the quality of the collected eggs, it should also be noted that animal welfare will be significantly improved by replacing stripping with natural spawning - without the use of hormones. Furthermore, it should be noted that some fish species considered to be good candidates for aquaculture are so susceptible to handling that the only feasible method of obtaining embryos will be through natural spawning; two such species are included in the study. While the correct environmental cues will induce natural spawning in captive fish, the physical features of the holding tanks may be manipulated to reduce the negative behavioural traits which may impede courtship. To achieve this end for flatfish, each female will be provided with a “breeding nest”, a gravel-filled structure, while demersal round-fish species will be held in shallow raceways so broodfish populations can perform schooling behaviour along a high-speed current axis. Both features are expected to facilitate undisturbed courtship. Infra-red cameras will document fish behaviour in the system. The expected improvement of egg quality will be verified through the implementation of different methods.