▁two ▁scales ▁between ▁the ▁tip ▁of ▁the ▁pel vic ▁fins ▁and ▁the ▁anal ▁fins , ▁while ▁on ▁the ▁ro ach ▁there ▁are ▁five . ▁Also ▁the ▁skin ▁of ▁the ▁rud d ▁is ▁yellow ish ▁green , ▁while ▁the ▁ro ach ▁is ▁bl u ish ▁on ▁the ▁fl anks . ▁Also ▁the ▁u pt urn ed ▁mouth ▁is ▁visible ▁even ▁in ▁young ▁fish . ▁Furthermore , ▁the ▁rud d ' s ▁number ▁of ▁soft ▁ray s ▁in ▁the ▁d ors al ▁fin ▁( 8 – 9 ▁compared ▁to ▁ 1 0 – 1 2 ). ▁There ▁can ▁be ▁confusion ▁with ▁the ▁ide ▁also , ▁which ▁has ▁smaller ▁scales ▁however . ▁ ▁There ▁is ▁a ▁variety ▁of ▁the ▁common ▁rud d , ▁popular ▁among ▁p ond - keep ers , ▁known ▁as ▁the ▁golden ▁rud d , ▁which ▁has ▁a ▁gold - col oured ▁body . ▁ ▁The ▁rud d ▁can ▁grow ▁to ▁a ▁size ▁of ▁about ▁ 4 5 – 5 0   cm ▁with ▁an ▁average ▁of ▁about ▁ 2 5   cm . ▁ ▁The ▁d ors al ▁fin ▁and ▁p ector al ▁fins ▁are ▁grey ish ▁with ▁a ▁re dd ish ▁t int ▁and ▁all ▁the ▁other ▁fins ▁are ▁bright ▁red . ▁This ▁color ing ▁of ▁the ▁fins ▁is ▁the ▁feature ▁to ▁which ▁the ▁sevent e enth ▁century ▁name ▁‘ r ud d ’ ▁refers . ▁ ▁E col ogy ▁Rud d ▁prefer ▁clear ▁waters ▁rich ▁in ▁plants . ▁They ▁also ▁feed ▁on ▁aqu atic ▁veget ation ▁when ▁the ▁temperature ▁exceed