Mudskippers indicate the evolutionary transition of tetrapods from fishes. It is a useful indicator of the evolution of species from water to land. Mudskippers are predominantly found in the mangrove forests and mudflats of the into-west pacific region, Africa's tropical western coast, and Indian Ocean Ocean Coastlines. They are burrow dwelling and prefer swampy marshes, estuaries and the intertidal area for their living. They are also opportunistic feeders, meaning, they satisfy their dietary requirements according to the available food. They mostly feed on algae, detritus, diatoms, nematode, polychaete and eggs of fishes along with mud and sand particles.
Due to mudskippers' medicinal properties, it is used as traditional medicine or has commercial value for its consumption. They are also used as bait sometimes. They are known by various conventional names such as sakomo, nebesokera, canipo and vaetti uluvai in Tamil.
As Ecological Indicator
The intertidal and estuarine hearth is monitored by the abundance of Mudskipper, which has natural affection towards salinity and temperature variation. Mudskippers also contribute towards the growth of mangrove trees, when the population of mudskippers is abundant, which results in the provision of more nutrients for the development of mangroves. Mudskippers bioaccumulate pollutants by ingesting preys in the mudflat species. This ensures and maintains the intertidal, coastal and estuary health. Studies also show that mudskippers act as a biological indicator for oil pollution seen in Persian Gulf coastal areas. Periophthalmus waltoni's biological indicator response serves as the ideal candidate for bioindicator in the coastal regions and mudflats. Therefore, this species can be used for achieving sustainable development.
Similarly, at Kuwait, Periopthalmus Walton is a bioindicator for identifying bioaccumulation of metals. Metal toxicity and accumulation of metal toxicants like zinc, cadmium, lead and copper in mudskippers suggest that they are ideal biomonitors. It was observed that heir fins and liver accumulated the metals and therefore acted as biomonitors.
They are found in riparian areas with muddy and soft plains. They usually inhabit the areas that have rich benthic invertebrates and where the salinity is low. Rehabilitating coastlines with mangrove trees prove to improve the numbers of mudskippers found there. Mudskippers are known to alter the environmental conditions that enhance young mangroves' growth as they mix the soil with detritus. However, there are significant threats to the habitats in soil erosion, macroalgae, terrestrialization and lack of estuarine water, human interference, discharge of effluents, etc.
To determine habitat selection by the mudskippers, genomics studies were performed, and the comparative analysis among different species was conducted. It was found that different mudskippers inhabit different microhabitats and have other burrow construction methods.
Pattern of Behaviour
The growth rate is inversely proportional to the population density as the food availability decreases when there is population increase. Chinese Mudskipper can survive for two and a half days out of water. The mudskippers growth rate is affected when being exposed to pollution at the embryonic stage. Aquaporins play a significant role in adapting themselves to the terrestrial lifestyle. Mudskippers are observed to build mud walls to avoid overlapping territories which in turn reduces hostility. Mudflats are essential for the survival of the mudskippers, but global warming is a severe threat to the mudflats. A few mudskippers are more adapted and comfortable for the terrestrial lifestyle rather than the aquatic lifestyle. An example of this would be Periophthalmodon schlosseri whose gill arrangement are highly adaptable for air-breathing. Therefore they spend less time in marine habitats.
Mudskippers build walls for two reasons, to avoid hostility and assist in feeding. Building walls prevent the intervention of other neighbours from feeding on the diatoms present in the mud slopes.
It was discovered in a study that Mudskipper uses both body and pectoral fins for movement in the water and only pectoral fin for activity Inland. For survival, they rely on escapism, and these adaptations help them do so.
Mudskippers are herbivorous as well as omnivorous. When researchers studied Periopthalmus barbarous stomach, it was found that it contained mainly crab, fish scales and insects. This proves that mudskippers are opportunistic feeders. As mentioned earlier, their primary food choice includes diatoms, nematodes, polychaete, fish eggs, algae, detritus along with particles of mud and sand.
Mudskippers are ko=nown frothier high protein content and other nutrients. They are often used as traditional n=medicines in Malaysia or as bait or used for consumption. There is a growing demand for mudskippers at Narmada estuary, Gujrat, a local delicacy. Due to this high demand, the ecosystem can get disrupted due to the change and impact on biodiversity. Even though mudskippers have their fair share of nutritional benefits, researchers also warn about metal toxicity and. Bioaccumulation when consumed.
Threats looming over mudskippers
Mudskipper distribution and abundance have become vital for determining intertidal region health—mudskipper face menaces due to metal toxicity. When exposed to chromium, there is a direct effect on sodium, potassium and ATPase activity in Boleopthalmus dentatus. It also affects membrane activity, thereby causing metabolic stress. The shrimp effluents collected at the Persian Gulf's mudskipper habitat have indicated that it supports mudskipper enrichment. This helps them increase their species density and length. Even if there are severe changes and reduced dissolved oxygen, shrimp effluents create favourable physical conditions for mudskippers to thrive amongst these adversities.
Therefore, we can see that mudskippers are known to adapt to a range of environments. Inspire of this they are not well understood by the layman. This ignorance can and is potentially leading to a loss of these versatile species. Hence, I hope this small article has to lead you to become more aware of this walking fish and has managed to excite you with the versatility and adaptation f this less noticed creature.
A. Kumaraguru, R. Mary and V. Saisaraswathi, "A review about fish walking on land", Journal of Threatened Taxa, vol. 12, no. 17, pp. 17276-17286, 2020. Available: 10.11609/jott.6243.12.17.17276-17286 [Accessed 27 January 2021].