Breeding Biology of the Lake Chub, Couesius plumbeus, at Lac la Ronge, Saskatchewan

Abstract

Spawning of the lake chub, Couesius plumbeus (Agassiz), was investigated at Lac la Ronge from 1966 to 1968. Nonadhesive eggs were freely dispersed in rocky shallows in the tributary Montreal River during May and along rocky shores of the lake in late June. Temperature played a regulating role and most breeding activity occurred after the water reached 10 C. Some 4000 individuals were marked by finclipping and subsequent recaptures revealed that chubs migrated as much as 3 km in order to spawn in the river.Early arrivals in the river were cryptic. Males were somewhat aggressive during spawning but no territoriality was observed in the field. No nests were built and there was no parental guarding. Males outnumbered females on the spawning grounds and spawning activity was polyandrous. Males courted females by a combination of persistent pursuit and specially directed nudging. Sexual dimorphism was apparent in the larger pectoral fins, the more distinct dark lateral stripe, and the greater development of nuptial tubercles and orange breeding marks on males.Age-group III females made up 68% of the spawning population in 1968 and contributed 54% of potential recruitment. These fish were spawning for the first time at a mean total length of 95.1 mm. Age-groups V and over constituted 6% of the spawning females and contributed 13% of potential recruitment. The largest female captured was 147 mm total length.Certain fundamental aspects of the breeding behaviour were found to be inconsistent with that reported among established species in the genus Hybopsis. Inclusion of the lake chub within Hybopsis as has been suggested by some investigators is accordingly considered indefensible.