A review on mesopelagic fishes belonging to family Myctophidae

Myctophids are mesopelagic fishes belonging to family Myctophidae. They are represented by approx. 250 species in 33 genera. Called as "Lanternfishes", they inhabit all oceans except the Arctic. They are well-known for exhibiting adaptations to oxygen minimum zones (OMZ-in the upper 2,000 m) and also performing diel vertical migration between the meso- and epipelagic regions. True to their name, lanternfishes possess glowing effect due to the presence of the photophores systematically arranged on their body, one of the important characteristic adding to their unique ecological features. Mid-water trawling is a conventional method of catching these fishes which usually accounts for biomass approx. in million tones as seen in Arabian Sea (20-100 million) or Southern ocean (70-200 million). Ecologically, myctophids link primary consumers like copepods, euphausiids and top predators like squids, whales and penguins in a typical food web. Lantern fishes become a major part of deep scattering layers (DSL) during migration along with other fauna such as euphausiids, medusae, fish juveniles, etc. Like any other marine organisms, Myctophids are susceptible to parasites like siphonostomatoid copepods, nematode larvae etc. in natural habitats. They are important contributors of organic carbon in the form of their remnants and fast sinking faeces, which get deposited on ocean beds. Economically, they are a good source of protein, lipids and minerals, which is used as fishmeal for poultry and animal feed and as crop fertilizers. Few species are considered edible, but proper processing difficulties on a higher scale limit myctophids as human food. Myctophids have a life span of approx. 1-5 years and low fecundity rates (100-2,000 eggs per spawn). This trait is a disadvantage, if continuous utilization of their population, for e.g., for fish meal industries etc., occurs without giving them a chance to revive and recover. Hence, research in this area also should be given utmost importance. In this paper, we have tried to compile information and ideas from various sources of myctophid research around the world, particularly from the Indian Ocean, to understand their ecological and economic importance and also to put forth new ideas to bring about conservation and restoration of this vulnerable resource.