Photothermal manipulation of reproduction in Indian major carp: a step forward for off-season breeding and seed production

We report here for the first time significant advancement of sexual maturation and off-season breeding of Indian major carp (IMC) species, rohu (Labeo rohita), catla (Catla catla) and mrigal (Cirrihinus mrigala) through photothermal manipulation during winter at least 4–5 months prior to their normal spawning season (June–August). The spent fishes were subjected to different photothermal regimes such as long photoperiod in combination with above ambient water temperature (LP–AAT), simulated natural photoperiod with ambient temperature (SNP–AT) under controlled condition and natural photoperiod under pond condition (NP–AT). Both the sexes of the IMCs attained suitable gonadal maturity for induced spawning between 100 and 124 days of rearing under LP–AAT condition during winter months. However, the broods under the SNP–AT and NP–AT regimes did not show any sign of maturity of gonads. Matured females of all the species induced to spawn successfully and produced a similar quantity of eggs and spawns as reported in the case of pre-monsoon spawning in the species, except for mrigal. The spawning success of individual species ranged between 66.6% and 100%. The results clearly reveal that the photothermal manipulation does modulate physiological rhythm for altering spawning times and provides scope for off-season production of spawn, fry and fingerlings of IMC almost throughout the year to facilitate aquaculture in a most effective way.