Background/Aims
Understanding how reproductive behaviour translates into realised reproductive success is critical for managing captive breeding programmes. In Murray cod, genetic studies have revealed polygamous mating despite historical assumptions of monogamy. Captive breeding research has shown that unequal reproductive contributions can reduce effective breeder numbers and genetic diversity. Although Murray cod are widely used in breeding programmes, the behavioural mechanisms underpinning reproductive success remain poorly understood.
This study quantified relationships among nest-box visitation, mating patterns, and reproductive success within a captive Murray cod (Maccullochella peelii) breeding population by combining Passive Integrated Transponder telemetry with genome-wide single nucleotide polymorphism parentage analysis.
Methods
Seventeen PIT-tagged broodfish were monitored over an 83-day study period, generating 4,568,771 detections across five nest boxes. These data were used to quantify nest-box visitation and temporal variation across diel and seasonal scales, and to assess the influence of short-term environmental conditions on visitation. Seven spawning events were recorded, and 281 larvae were genotyped using DArTseq to reconstruct parentage and quantify reproductive output, broodfish size effects, and offspring genetic diversity.
Results
Nest-box visitation increased during the spawning period and was further influenced by diel timing and short-term environmental conditions. Visitation was strongly male-biased and uneven among individuals. Reproductive success was strongly associated with total nest-box visitation, with one male siring 163 of 278 assigned offspring across five spawning events. Parentage analysis revealed flexible mating strategies, including single-pair spawning and mixed-parentage clutches, with evidence of within-clutch polygynandry and reproductive skew. Effective breeder number was lower than census size, particularly among males, although overall offspring genetic diversity remained high.
Conclusion
These findings show that nest-site behaviour can strongly shape reproductive outcomes in captive Murray cod. Integrating behavioural monitoring with parentage analysis provides a practical framework for identifying over-represented breeders, managing kinship risks, and improving genetic management in hatchery breeding programmes.