Zig-zag eel

Mastacembelus armatus is a large elongated fish that has a snake-like body without pelvic fins. Its anal and dorsal fins are elongated and are connected to the caudal fin. The dorsal fin is preceded by numerous spines. A pattern of black dots is located on either side of the dorsal fin mimicking the pattern of the sandy and rocky substrates it dwells among to hide from predatory fishes looking down from above. The back is dark beige in color while the head is silver-beige. The body's color is dull brown and the belly is a lighter shade of brown. The brown tones of the zig-zag eel's coloration grant an advantage in concealing itself from both predators and prey in the turbid water environments that it inhabits. The body may also be marked with brown circular patterns. The body also has one to three darker longitudinal zigzag lines that connect to form a distinct reticulated pattern that is restricted to the dorsal two-thirds of the body. The eyes have brown stripes running laterally through them. The age of a zig-zag eel can be determined by the length of the fish and the radius of its scales which have a linear relationship. As these fish age they develop growth ring on their scales called annuli. These rings form during the annual monsoon season and the fish faces changes in food availability and spawning pressures that limit growth during this season. Zig-zag eels sampled from their natural habitat average about four annuli maximum on their scales suggesting a longevity of four years in the wild. Despite its eel-like appearance, Mastacembelus armatus is not considered a true eel as it belongs to the order synbranchiformes rather than anguiliformes. == Habitat and distribution ==

Mastacembelus armatus are nocturnal fish that thrive in highland streams, lowland wetlands, still waters, coastal marshes and rivers with sandy or rocky riverbeds and heavy vegetation. These potamodromous fish migrate throughout rivers and streams. Their migratory behavior results in genetic variation between populations that are not connected through river systems or do not interact along their migratory routes. Most zig-zag eels best tolerate a pH range of 6.5–7.5 and prefer tropical water temperatures between 22 and 28 °C. However, Some populations live in rivers at higher elevation where the water is supplied by snow melt from the Himalayas and can withstand much cooler water temperatures. They are common during the tropical summer months and will dwell in canals, lakes and other floodplain areas during the flood season. Mastacembelus armatus fulfils the role of an intermediate predator in the freshwater ecosystem. Reduction in populations of this species poses a risk of trophic cascade. In an aquarium setting, they require live foods in their diet such as live fish, tubifex worms, brine shrimps, mosquito larvae, frozen bloodworms, cyclops, krill and ocean plankton. ==Conservation status==

Globally categorized as least concern yet endangered in Bangladesh as of 2000. Considered vulnerable in Telangana and Tamil Nadu but least concern in Pakistan. Threats to the population of zig-zag eels includes habitat loss, pollution and overfishing. Heavy metal and metalloid pollutants in the rivers Mastacembelus armatus inhabits results in depletion of tissue glutathione content, increase in liver peroxidation, and decreased antioxidant enzyme activity. These three conditions are direct impacts of oxidative stress caused by chemical pollutants and raise concern for bioaccumulation of toxins. Consumption of fish exposed to these pollutants can have adverse health effects and efforts to reduce river pollution to benefit human health supports the health of this species as well. ==In aquarium==

Maintenance Mastacembelus armatus are bottom dwellers and substrate diggers. ==References==