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

Abstract

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