Many oxudercine species face rapid and drastic changes of environmental salinity and are euryhaline.
Osmoregulation in hyperosmotic environment (i.e. sea water) is realised through the accumulation of free amino acids (FAA) and ammonia (NH3) in muscles (Iwata et al., 1981). The increased osmolality of body fluids limits the passive intake of ions. Salts in excess are excreted through the gills by means of the "chloride cells" (Evans et al., 1999).

In Periophthalmus modestus, and probably in all congeneric species that have strongly reduced gills, this process takes place also in some cutaneous areas (i.e. behind pectoral fins) through specialized, mitochondria-rich cells (Yokota et al., 1997; Sakamoto et al., 2000; Sakamoto & Ando, 2002).

Osmoregulation at low salinity levels instead (hyposmotic environment) seems at least partly behavioural: emergence would compensate for the excessive hydration through cutaneous evapotranspiration (Clayton, 1993).

Juveniles of Periophthalmus koelreuteri (= P. waltoni) clinging to the wetted zone of the shaded side of wooden planks projecting from the mudflat at high tide;
dotted area= sea water; continuous hatching= wetted zone; broken hatchings= dry wood; temperatures of the different surfaces are indicated. Due to the evapouration, the humid zone has lower temperatures than water and dry wood.
Drawing: G. Polgar, redrawn from Tytler & Vaughan, 1983, with permission from the Blackwell's Publ.

Other noticeable specializations are found in amphibious oxudercine gobies, which face some of the harshest temperature gradients experienced by fish. In fact, the higher heat capacity of water makes the aquatic environment much more thermically stable than the subaerial one.

Euritherm species thermoregulate through coloration changes (Stebbins & Kalk, 1961), evaporative cooling (Taylor et al., 2005) and behavioural thermoregulation. B. dussumieri adopts a horizontal position with its body at right angles to the sun, to increase its body temperature during cooler days (Clayton & Vaughan, 1988)

Burrows may also play a fundamental role in temperature balance: there can be differences of up 11-13 °C between surface and burrow conditions (Tytler & Vaughan, 1983; Aguilar, 2000).

It is interesting to note that several oxudercine species which live in geographic areas with a seasonal climate, can aestivate (Pseudapocryptes, Periophthalmodon spp.) or hibernate (Periophthalmus, Boleophthalmus, Apocryptodon and Scartelaos spp.), taking refuge in their burrows waiting for appropriate weather conditions (Clayton, 1993, Townsend & Tibbetts, 1995; Ishimatsu et al., 2000; Yuko Ikebe, pers. comm.), not unlike some modern aquatic sarcopterygians (dipnoans: Graham, 1997).