Environmental salinity and osmoregulatory processes in cultured flatfish

Abstract

The aim of this study was to carry out a comparative analysis of the osmoregulatory properties and associated energy metabolism of euryhaline flatfish species that are cultured in the world. Culture of flatfish (pleuronectiformes) requires stage-and species-dependent osmotic conditions for rearing. Additionally, geographic origin of broodstock animals is another factor to be taken into account for the culture of pleuronectiformes. Larval and juvenile stages of many flatfish species are cultured in large nurseries situated in estuaries and shallow marine habitats, where the environmental salinity is close to the iso-osmotic point of their internal milieu. This fact implicates an advantage in terms of energy savings for osmoregulatory purposes. Thus, this 'saved' energy can be derived to other physiological processes, such as somatic growth. However, this scientific presumption does not always results in an optimal growth for many flatfish species. Indeed, iso-osmotic culture conditions can evoke a higher allostatic load than that in the usual hyper-osmotic environment where flatfish species live wildly. Optimization of flatfish culture thus requires adjustments of the osmotic culture conditions to the specific osmoregulatory and metabolic demands that eventually determine the allostatic load and consequently condition growth rates. In this sense, the geographical location of aquaculture farms and the osmoregulatory-based selection of the species to be cultivated in a particular area become critical factors to be considered for optimal flatfish culture.

Environmental Salinity Affects Growth and Metabolism in Fingerling Meagre (Argyrosomus Regius)

“…Estuaries are associated with the life history of the meagre, and meagre juveniles are mostly found in brackish waters [10]. Moreover, responses to salinity are also influenced by the age of the fish [24]. These prior descriptions are supported by the present study, which found that three-month-old fingerlings presented better growth rates in brackish water (iso-osmotic salinities, 12 ppt) compared to seawater (SW, 39 ppt).…”

“…However, A. japonicus juveniles weighing less than 10 g perform best at a salinity of 35 ppt [22], while 10-20-day-old larvae show optimum growth at 5-12.5 ppt [23]. This information supports previous studies findings that the salinity for optimum growth can vary with fish age [24]. While some information exists for the culture of A. regius juvenile fish in cages and earthen-ponds with natural seawater conditions [3,[25][26][27], there is less information available for the effects on A. regius production at different salinities during the early lifecycle stages [19].…”

“…However, major differences were found when comparing A. regius to the related A. japonicus, a species that presents optimum growth at 35 ppt for individuals weighing less than 10 g [22]. This difference between closely-related fish species highlights the importance of separately studying each species to determine the best environmental salinity for growth [24].…”

Narrowing the Range of Environmental Salinities Where Juvenile Meagre (Argyrosomus regius) Can Be Cultured Based on an Osmoregulatory Pilot Study

“…This euryhaline response coincides with what was described in the sciaenid shi drum, Umbrina cirrosa [34], the European seabass, Dicentrarchus labrax [35] and the sub-Antarctic Eleginops maclovinus [36]. However, other euryhaline species cultured in Europe such as Sparus aurata, Dicologoglossa cuneata and Scophthalmus maximus manage to maintain constant plasma osmolality levels within a narrower range of salinities, from brackish water close to the iso-osmotic point of these species to seawater [23,37,38], while Solea senegalensis, Scophthalmus rhombus and Pagrus pagrus show increasing plasma osmolality as environmental salinity increased [39][40][41].…”

Dynamics of early life‐history stages of fish along an estuarine gradient

“…Additionally, the osmoregulatory ability likely plays an important role in defining flatfish species and developmental stage‐specific distribution (Schreiber, ). Several studies (e.g., Ruiz‐Jarabo et al., ; Schreiber & Specker, ; Yamashita, Tanaka, & Miller, ) suggest that short‐term tolerance to salinity ranging from high for early larvae, decreases dramatically during mid‐larval development, then achieves adult‐like levels (usually relatively high tolerance) by the completion of metamorphosis. The data obtained in the present study support these observations, since the lower estuary, which is the closest region from the coast, had the greatest abundances of Achirus sp.…”