Salinity tolerance of two tropical fishes, Oreochromis aureus and O. niloticus. I. Biochemical and morphological changes in the gill epithelium

Abstract

Cichlids of the genus Oreochromis are fish of economic importance in African countries. They tolerate brackish water, however, with great variations between species. In this work, two species, both from the Ivory Coast but of different origins, O. niloticus (field and laboratory strains) and O. aureus (field strain) were compared during osmotic challenges (10, 20 and 30%o salinity) in order to provide physiological support for their specific behaviour when confronted with natural hypertonic environments. Tolerance to salinity was assessed by correlated observations on gill structure, plasma sodium levels and gill Na+/K+ ATPase activity. In fresh water (FW), all fish presented a gill epithelium structure characteristic of FW stenohaline fish: no chloride cells (CC) on the lamellae and few CC on the filaments. An increase in external salinity induced the proliferation of CC on filaments, a feature typical of seawater teleosts. This change in gill structure was accompanied by an increase of gill Na+/K+ ATPase activity. In the most tolerant strains, plasma Na+ did not change, indicating successful ion regulation in the hypertonic media. With regard to potential interest of field strains in fish culture, O. aureus acclimated more easily to brackish water than O. niloticus. Interestingly, O. niloticus, kept for several generations in the laboratory, performed best in our challenge studies. Plasma Na+ levels and gill CC proliferation upon transfer to an isotonic medium may be the parameters of choice when testing these fish for their response to a salinity change.

Acclimation trials of juvenile Italian sturgeon to different salinities: morpho-physiological descriptors

“…An increased number and/or size of the interlamellar chloride cells is described for euryhaline teleosts during adaptation to SW (Laurent & Hebebi, 1989;Cioni et al, 1991;Avella et al, 1993). On the other hand, a degeneration and disappearance of lamellar chloride cells, that are linked to the ion pumping capacity of the gill in FW, was reported for the Atlantic salmon during its migration to the sea (Bornacin et al, 1987).…”

Morphological variations of wild populations of Nile tilapia (Oreochromis niloticus) living in extreme environmental conditions in the Kenyan Rift-Valley

“…This species has been recognized for its ability to tolerate a wide range of salinity, dissolved oxygen and temperature (Farmer and Beamish 1969;Avella et al 1993), high fecundity and rapid growth rate (Welcomme 1967) and an omnivorous mode of feeding (El-Sayed 1999). Due to these attributes, the species has the ability to adapt rapidly to new environments, showing a wide range of biological responses to different environmental conditions both in culture and in nature (Schofield et al 2011;Grammer et al 2012).…”

Morphological changes in the gills of Lophiosilurus alexandri exposed to un‐ionized ammonia

“…Modifications in the concentration of NaCl (Perry & Laurent, 1989) and of ammonia (Wajsbrot et al, 1993), in addition to variations of temperature (Boyd et al, 1980), pH (Wilkie & Wood, 1994) and salinity (Avella et al, 1993), among other factors, induce morphological modifications or cellular adaptations, related to the plasticity of the branchial epithelium (Laurent & Perry, 1990).…”