Body is elongated, devoid of scale; herring-shaped in younger stages and bulky at the belly in adult. A median fontanel is extending along the entire length of the head; shallow in front and somewhat deeper behind. Occipital process tapers to a fine point posteriorly and separated from the basal bone of the dorsal fin. Teeth in jaws are villiform; those on the palate are arranged in a crescentic band. Mouth is terminal; lower jaw is a little longer, snout is rather broad. Gape of mouth is more than half of the head length; mouth cleft does not extend below eye. Eyes are with narrow adipose lids. A pair of maxillary barbels is present; mandibular barbels are rarely seen. Two dorsal fins are present; the first one is with a weak and finely serrated spine and few rays and is as long as the head behind the middle of the eye; the second dorsal is adipose. Pectoral fin spine is stronger, serrated along both edges and is as long as head without snout. Pelvic fin arises under the posterior dorsal rays and nearly reaches the anal. Anal is long; extending anterior half of the body. Caudal fin is deeply forked. Body is bluish in color along the back and silvery on the sides; lips are red; fins are stained with grey. Fin formula: Fin rays: D1. (1/7), D.O; P.1/11-13; V.6; A.40-46 (4/35-44); C.17 (Bhuiyan, 1964); D. 1/7; P1 1/12-13, P2. 6; A 41-46. D1. 1/7; D2 O; P1 1/11-13, V 6; A 40-46 (4-36/42). S. silondia is widely distributed in India, Bangladesh, Nepal, Pakistan and Myanmar (Talwar and Jhingran, 1991). It is a very common food fish of West Bengal where its flesh is prized. It is a delicacy in Punjab and Haryana. Previously abundant in the rivers, streams, canals, reservoirs, lakes, swampland (beels, haors and baors) and ponds of Bangladesh (IUCN Bangladesh, 2000), India and Pakistan, the species is currently declining in the main streams. S. silondia is a demersal and amphidromous fish that generally occur in shoals. Commonly found in estuaries and rivers (mainly fluviatile) but also be alive in tanks and large reservoirs (IUCN Bangladesh, 2000). This fish species is quite frequent in the estuarine zone of river Hooghly (Gopalakrishnan, 1971). It inhabits in the estuaries of India and Myanmar; and ascends the large rivers almost to their sources. Due to its long range tolerance for salinity and temperature and long migratory habit, the silondia often freshwater regions of rivers and reservoirs. They are also found to flourish well in tanks (Chondar, 1999). Gregarious and moves in shoals (IUCN Bangladesh, 2000). Inhibits estuaries and rivers throughout Bangladesh. Carnivorous feeding habit of Silonia silondia has been reported by all previous workers (Hora, 1938, Gupta, 1981 and Karamchandani, 1957). The pre and post larvae of this fish species up to 10 mm size used to feed exclusively on zooplankton. The carnivorous feeding habit used to develop right from the early fry stage. 11-25 mm size fry takes carp fry, copepods and nauplius. Voracious piscivorous tendency develops in the fingerling stage when they predate on fry and fingerling of other fishes. Adults consume both fishes and bottom biota like prawns, crabs, molluscs, insects etc. (Karamchandani, 1957). Hora, 1938 has reported the young silond below 10 cm size from the river Hooghly to feed on prawns and young fish, while adults mainly consume Hilsa ilisha and other fishes. Menon and Chacko (1958) and Agarwal and Tyagi (1969) have documented the presence of fishes, crustaceans, gastropods and insects in the gut content of silond fish. Carnivorous and voracious feeder (Bhuiyan, 1964; IUCN Bangladesh, 2000) and for this it also causes considerable damage to the fisheries. Takes fish, rotten organic matters etc. as food (Shafi and Quddus, 2001). The information on genetic parameters of S. silondia is very limited. Cytochrome b (1140 bp) and ATPase 6/8 (842 bp) genes were analyzed by Mandal et al. (2014) reported high level of genetic differentiation within populations of this fish. The sequence alignments of cytochrome b and ATPase 6/8 genes revealed 13 and 11 different haplotypes, respectively. The sequences of both the mitochondrial regions revealed high haplotype and low nucleotide diversities. The patterns of genetic diversity and haplotype networks clearly indicated two distinct mitochondrial lineages; however, haplotypes from both the lineages were not specifically assigned to any population. The results confirm the utility of molecular markers generating baseline information, useful for planning effective strategies for conservation, management and sustainability of Silond catfish fishery. The species-specific microsatellite markers were used by Mandal et al. (2016). The validated markers were used to genotype individuals from four distant rivers. To develop de novo microsatellite loci, an enriched genomic library was constructed for this fish species using affinity-capture approach. The markers were validated for utility in population genetics. A total number of 76 individuals from four natural riverine populations were used to generate data for population analysis. The screening of isolated repeat sequences yielded eleven novel polymorphic microsatellite loci. The microsatellite loci exhibited high level of polymorphism, with 6-24 alleles per locus and the PIC (Polymorphic Information Content) value ranged from 0.604 to 0.927. The observed (Ho) and expected (He) heterozygosities ranged from 0.081 to 0.84 and 0.66 to 0.938, respectively. The ANOVA analysis indicated significant genetic differentiation among riverine populations (Fixation Index, FST = 0.075; P < 0.0001) with maximum variation (92.5%) within populations. Cross-priming assessment revealed successful amplification (35-38%) of heterologous loci in four related species viz. Clupisoma garua, Clupisoma taakree, Ailia coila and Eutropiichthys vacha. The results demonstrated that these de novo polymorphic microsatellite loci are promising for population genetic variation and diversity studies in S. silondia. Cross-priming results indicated that these primers can help to get polymorphic microsatellite loci in the related catfish species of family Schilbidae. Maximum length recorded 26 cm (Bhuiyan, 1964), 100 cm (Talwar and Jhingran, 1991), 80 cm (Rahman, 1989 and 2005) and 80-100 cm (IUCN Bangladesh, 2000). Maximum length and weight recorded by Rahman (1989 and 2005) 790 mm and 3.9 kg fish from the Gacher Duhar beel in Sylhet (Bangladesh). S. silondia is commercially fished, but has a very low resilience to fishing pressures, according to parameters suggested by the American Fisheries Society. Its minimum population doubling time is more than 14 years. It contributes to the commercial fishery in the Hirakud reservoir, Orissa, India, where available information indicates a decreasing trend in the populations of carnivores, of which S. silondia is a part (Devi and Boguskaya, 2009). In addition, Mishra et al. (2009) reported that over-exploitation is a potential major threat as this species is heavily used as a food fish and they recorded a mean decline of 29.2% in wild catches in southern West Bengal for the period of 1960-2000.