This paper provides length-weight relationships (LWRs) for four freshwater cyprinid fish species, namely Barilius bendelisis (Hamilton, 1807), Bangana dero (Hamilton, 1807), Chagunius chagunio (Hamilton, 1807) and Labeo dyocheilus (McClelland, 1839) from the Kosi River, a tributary of the River Ganga in northern India. Altogether 848 specimens were caught bimonthly (for B. bendelisis) and quarterly for the other three species between March 2013 and December 2014 using cast nets (9 m length, 9 m width and 1/2 cm mesh size). LWRs for two of the four species (B. dero and C. chagunio) are recorded for the first time. The present study results will be useful for fishery researchers, management and conservation in this least-explored tributary of the Ganga River Basin.

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During its course of 2,525 km, the River Ganga flows through the variant topography, ecological, and environmental conditions that harbor huge range of floral, faunal, and fish diversity. The ecological condition and biodiversity of upper, middle, and lower stretches of the river are different from each other. Increases in anthropogenic activities on Ganga have resulted in a decrease in quality and quantity of its water, which ultimately led to change in its biodiversity. Menon (1974) listed 141 fish species occurring in the Ganga River system belonging to 72 genera, 30 families, and 11 orders. Recent studies reported 143 fish species from the River Ganga (Das et al., 2014; Sarkar et al., 2011) including cold water, freshwater, and estuarine fishes. In this article, a critical comparison is made on the availability of an important fish group, the Indian Major Carp (IMC), of the Ganga River during different decades, starting from 1956 and annual yield between 2005 and 2018. Average annual IMC landing during 1955–1967 was recorded as 90.85 ton, with maximum (131.3 ton) during 1964–1965 and minimum (54.0 ton) in the year 1958–1959. There was generally an increasing trend of IMC landing during 2005–2018, but it has reduced to one‐third in comparison to the time period of 1956–1967. The analysis shows that catch as well as species composition of IMC had been changed over the period of time due to changes in hydrological regime and ecology of the river. The reason in totality of this change is a focused theme of this paper.

An attempt was made to advance the spawning period of Labeo dyocheilus (McClelland, 1839) by pretreatment with the synthetic gonadotropin releasing hormone analogue, Ovatide. Total 12 females and 24 males (1: 2 ratio) were used for breeding operations conducted during 30th May to 30th June 2016 comprising six sets. Female fishes of set I to IV were pretreated with intramuscular injection of the ovatide at the rate 0.3 ml kg-1 body weight twice at an interval of two weeks while males were injected @ 0.1 ml kg-1 body weight once before 15 days of induced breeding trial for achieving advance maturity and spawning during pre-spawning phase. Fishes of set V and VI were not subjected to any pretreatment with ovatide. On 30th of June all the six breeding sets were were treated with ovatide for induced spawning. Female and males were injected at 0.7 ml kg-1 and 0.3 ml kg-1 of body weight, respectively and left overnight in FRP tanks for spawning. Results indicated that in sets I to IV, fishes successfully spawned and fertilised eggs were collected in morning hours whereas fishes of set V and VI failed to spawn. Fertilisation and survival rates recorded were 79-82% and 67-71%, respectively. Results indicated that treatment of ovatide during prespawning phase is beneficial for advancing the gonadal maturity, successful induced spawning and prolonging the breeding period which may play a key role in production of substantial quantity of seed of L. dyocheilus.