Effects of day and night on swimming, grazing and social behaviours of rohuLabeo rohita(Hamilton) and common carpCyprinus carpio(L.) in simulated ponds

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AbstractDiel rhythmicity of grazing, swimming, resting andsocial interactions of rohu (Labeorohita)(weight66.5^68.3g) and common carp (Cyprinus carpio)(79.9^82.0g) were observed in1m 2 simulated ponds usingvideoimages. Fishbehaviour was monitored duringafull24-hperiod,startingat08:00hourswitha15-minrecording, whichwas repeated every 3h. Rohu spentmoretimegrazingduringthedaythanatnight.Graz-ingactivity peakedat thebeginningandat the endofthe day. Grazing and resting of rohu were negativelycorrelated.Commoncarpgrazeddayandnight,show-ing no distinctgrazing peak. Considering thegrazingtime of rohu and common carp, a feeding schedulewithtwofeedingtimesat07:30and16:30hoursmightbeappropriateforbetterfoodintakeandconversioninrohu^commoncarppolyculturesystem.Keywords: swimming, grazing, behaviour, rohu,commoncarpIntroductionTogether, rohu Labeo rohita (Hamilton) and commoncarp Cyprinus carpio (L.) contribute 26% (rohu 11%,commoncarp15%)ofthetotalworldfreshwateraqua-culture production outside China (FAO 2005). Nowa-days, rohu^common carp polyculture is being widelypracticed in South Asia. Rohu is a highlyappreciatedconsumption ¢sh, fetching good market prices (Dey,Paraguas, Bhatta, Alam, Weimin, Piumsombun,Koeshandrajana,DungSRahman,Wahab& Verdegem 2007), while common carp is gainingquick popularity as a bottom feeder in South Asiabecause it has a faster growth rate than the nativebottom feeder mrigal Cirrhinus cirrhosus (Bloch)(Milstein,WahabRRahman2006).The eiects of addition of arti¢cial feed and diier-ent densities of common carp on natural food avail-ability, food intake and growth and production inrohu ponds were studied (Rahman, Verdegem,Nagelkerke,Wahab, Milstein & Verreth 2006). It wasobservedthatbotharti¢cialandnaturalfoodsareim-portant for the growth of rohu and common carp.Thepondstudyshowedsynergisticeiectsonnaturalfood availability in rohu^common carp polyculture.The question was raised as to whether the observedsynergism was mainly caused by increased naturalfoodavailabilityorbyachange in feedingbehaviour.Behaviouralstudiesinpondsaredi⁄cultduetohighturbidityand, consequently, low visibility.Therefore,to be able to observe the feeding behaviour, pondtreatments were simulated in aquaria.The eiects ofarti¢cial feed applicationand diierent stocking den-sities of common carp (0, 1 and 2tank