The fish that skips and crawls on land

Mudskippers, a group of unique amphibious fish, stand out as marvels of evolutionary adaptation. They live in the intertidal habitats of mudflats and in mangrove ecosystems. They can move on land and feed, then return to water to breed and avoid predators.

They have a high degree of specialisation to amphibious life, relative to all living and extinct aquatic vertebrates. The subfamily Oxudercinae includes 10 genera and 40 species. They occur along the muddy shores of the intertidal areas in estuarine habitats and mangrove swamps of East Africa and Madagascar, east through the Sundarbans of Bengal, Southeast Asia to Northern Australia, southeast China and southern Japan, up to Samoa and Tonga islands. Out of 10 genera, except Zappa, nine are found in India, in the east and west coasts.

Although all mudskippers are found in the intertidal areas and estuaries, their distribution is different in terms of the species adaptability to the environment. For example, the Scartelaos histophorus species is generally found below the low tidal line where it gets the soft mud with higher amount of clay. The species, Periophthalmus magnuspinnatus is found in high tide line areas. Mudskippers show comparatively lesser density in the rainy season particularly from June to October, than other seasons.

In Gujarat and Maharashtra, mudskippers are called levata fish and are consumed by rural coastal communities. During the lockdown due to the Covid-19 pandemic, the demand of levata suddenly increased due to the myths surrounding the medicinal properties in the flesh of this fish.

Living off water

These amphibians can adapt to challenging environments, offering insights into the complexities of evolutionary biology. They are equipped with specialised pectoral fins that function as limbs, allowing them to move efficiently across mudflats and mangrove roots. This adaptation is crucial for navigating the intertidal zones where they reside.

Their ability to breathe through both gills and moist skin further exemplifies their adaptability, as it facilitates survival during periods of low tide, when they are exposed to air.

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Basking in the sun

Mudskippers bask in the sun during low tides to regulate their body temperature and prevent dehydration. This helps them maintain their physiological functions and avoid desiccation (drying out), which is crucial for survival in the intertidal zone. Basking allows them to absorb moisture from the environment, particularly through their skin, helping prevent dehydration.

To select the basking sites, they choose elevated locations such as rocks or mangrove roots. These spots offer exposure to sunlight and facilitate effective thermoregulation. Basking sites can also become areas for social interactions. Mudskippers may gather in these locations, displaying behaviours related to territoriality, courtship and communication. The timing and duration of basking vary based on environmental conditions.

Basking can also be part of courtship rituals, where males display their vibrant colours to attract potential mates. Some mudskipper species engage in intricate mating dances which involve specific movements and patterns that serve as a form of communication between potential mates. Their sounds which can range from clicks to chirps, contribute to the communication between males and females. Vocalisations may signal readiness to mate or play a role in establishing and maintaining pair bonds.

Females respond to the courtship displays of males. Their choice of mate may be influenced by the quality of the display, the condition of the male’s territory and other visual and auditory cues. Successful courtship increases the likelihood of successful reproduction. This extends to the nesting phase, where males prepare and defend nests for the deposition of eggs. Females may inspect potential nesting sites and successful courtship is often followed by the female depositing her eggs in the chosen nest. After the females deposit eggs in burrows, the males guard the nests, providing protection against predators and ensuring a higher chance of offspring survival.

Males engage in behaviours to oxygenate the eggs. This may involve fanning the eggs with their pectoral fins, ensuring proper oxygen exchange for the developing embryos. Oxygenation is critical for the successful development of the eggs in the intertidal environment. Mudskippers maintain the right level of moisture in the nesting area to prevent desiccation of the eggs. This is particularly important during low tide when the nest may be exposed to air. Males may dampen the nesting site to ensure a suitable environment for the eggs.

The duration of male parental care varies among mudskipper species but generally extends until the eggs hatch. During this brooding period, males remain vigilant, continuously guarding and caring for the developing embryos. The brooding period is a critical phase for the survival of the offspring.

After the eggs hatch, some mudskipper species continue to provide postnatal care. This may involve guarding and guiding the newly hatched larvae to suitable areas for feeding and shelter.

Male mudskippers actively deter potential predators from the nest. Their territorial behaviour extends to protecting the offspring, ensuring that the young mudskippers have a higher chance of reaching maturity. Understanding parental care in mudskippers highlights the intricate strategies these amphibious fish employ to ensure the survival of their offspring in the intertidal environment. The collaborative efforts of males in nest construction, guarding and post-hatching care contribute to the overall success of their reproductive endeavours.

Territorial behaviours

Female mudskippers are often attracted to males with well-established and defended territories, as it signifies the ability to provide a safe environment for nesting and raising offspring. Intense competition between males for prime territories is common. Conflicts may arise as males attempt to expand or defend their turf, leading to confrontations that involve physical displays and, in some cases, actual combat.

The size of the territory can influence the number of potential mates and available resources. Territorial behaviour is often more pronounced during the breeding season. Outside of this period, territorial disputes may decrease as the need to attract mates diminishes. Understanding their territorial behaviour provides insights into their reproductive strategies and social dynamics.

Ecological significance

Mudskippers play a crucial role as ecosystem engineers, influencing sediment composition and promoting nutrient cycling in intertidal zones. They play a key role in between benthic fauna and avifauna. They are dependent on small crustaceans and various algae such as diatoms and are also an important food source for avifauna, particularly coastal birds, including the migratory bird species.

The burrows they construct provide shelter for other small organisms in the intertidal environment. In mangrove habitats, their burrows help the mangrove roots receive oxygen.

Due to their sensitivity to environmental changes, mudskippers serve as indicator species, reflecting the health of intertidal habitats. Monitoring mudskipper populations, therefore, can provide insights into the impacts of climate change on a landscape and habitat degradation. Understanding the nuances of mudskipper biology not only contributes to scientific knowledge but also emphasises the importance of preserving intertidal habitats for the diversity of life they support.

CITATION:

Mithila Das and Sharat K Palita (2015). Record of six species of Mudskippers (Gobiidae: Oxudercinae) from the mangroves of Bhitarkanika, Odisha, east coast of India. Indian Journal of Geo-Marine Sciences 44(9): 1294-1301.

Jignesh R. Kanejiya, Devendra A. Solanki and Bharatsinh M. Gohil  (2017). Distribution of mudskippers in the mudflats of  Hathab Coast, Gujarat, india. Cibtech Journal of Zoology ISSN: 2319–3883 (Online) An Open Access, Online International Journal Available at http://www.cibtech.org/cjz.htm 2017 Vol. 6 (2) May-August, pp.1-9/Kanejiya et al.

Kannan Vaithianathan is a wildlife biologist and Kapil Kumar Ingle is a marine biologist.

Banner image: Dussumier’s mudskipper. Boleophthalmus dussumieri. Photo by Vaithianathan Kannan.