Adaptations of amphibious fish for surviving life out of water

Abstract

There are a small number of fish species, both marine and freshwater, that exhibit a truly amphibious habit that includes periods of aerial exposure. The duration of emersion is reflected in the level of physical and physiological adaptation to an amphibious lifestyle. Fish that are only briefly out of water retain predominantly aquatic attributes whereas there are semi‐terrestrial species that are highly adapted to prolonged periods in the aerial habitat. Desiccation is the main stressor for amphibious fish and it cannot be prevented by physiological means. Instead, amphibious fish resist excessive water loss by means of cutaneous modification and behavioural response. The more terrestrially adapted fish species can tolerate considerable water loss and may employ evaporation to aid thermoregulation. The amphibious habit is limited to fish species that can respire aerially. Aerial respiration is usually achieved through modification to existing aquatic pathways. Freshwater air‐breathers may respire via the skin or gills but some also have specialized branchial diverticula. Marine species utilize a range of adaptations that may include modified gills, specialized buccopharyngeal epithelia, the intestine and the skin. Areas of enhanced respiratory activity are typified by increased vascularization that permits enhanced perfusion during aerial exposure. As with other adaptations the mode of nitrogenous elimination is related to the typical durations of emersion experienced by the fish. Intertidal species exposed on a regular cycle, and which may retain some contact with water, tend to remain ammoniotelic while reducing excretion rates in order to prevent excessive water loss. Amphibious fish that inhabit environments where emersion is less predictable than the intertidal, can store nitrogen during the state of emersion with some conversion to ureotelism or have been shown to tolerate high ammonia levels in the blood. Finally, the more amphibious fish are more adapted to moving on land and seeing in air. Structural modifications to the pectoral, pelvic, dorsal and anal fins, combined with a well‐developed musculature permit effective support and movement on land. For vision in air, there is a general trend for fish to possess close‐set, moveable, protruberant eyes set high on the head with various physical adaptations to the structure of the eye to allow for accurate vision in both air and water.

Regionalization of patterns of flow intermittence from gauging station records

“…Aquatic and terrestrial species colonize and emigrate from intermittent rivers in response to shifts between wet and dry habitat (Acuña et al, 2005;Corti and Datry, 2012;Datry et al, 2012;Davey and Kelly, 2007;Steward et al, 2011). A smaller number of intermittent river specialists persist through multiple wet-dry cycles; this group includes aestivating fish and encysting invertebrates (Kikawada et al, 2005;Perry et al, 2008;Sayer, 2005). The alternating occupation of habitat by aquatic and terrestrial species means that the time-averaged biodiversity of intermittent segments can exceed that of perennial segments (Katz et al, 2012).…”

Food preference of the giant mudskipperPeriophthalmodon schlosseri(Teleostei : Gobiidae)

“…Another possibility is female P. schlosseri has been chased off from the male's burrow after laying their eggs. According to Sayer (2005) and Ishimatsu et al (2007), the female will be driven out from the burrow after mating. The male P. schlosseri assumes broodcare responsibilities.…”

Size variation of six species of oxudercine gobies along the intertidal zone in a Malayan coastal swamp

“…Larger evaporative losses in smaller individuals would result from higher surface to volume ratios; nonetheless, these would also increase diffusion rates through the integument, improving the efficiency of subaerial cutaneous respiration and excretion (Horn & Riegle 1981, Evans et al 1999. Water losses could also be compensated by the easier selection of appropriate conditions at the microhabitat level (Sayer 2005). At the synecological level, the spatial partitioning of different size and age classes amongst different habitat types can decrease niche overlap and increase resource partitioning (Spina 2000), being mediated either by interference competition or predation (e.g.…”