Strain‐specific effects of broodstock size on fecundity and offspring performance in bighead catfish ( Clarias macrocephalus Günther, 1864)

This study investigated the relationships among parental body weight, egg size and number, and offspring performance at the larval, juvenile and grow-out stages of bighead catfish (Clarias macrocephalus) in Mekong domesticated (Can Tho; CT) and wild (Ca Mau; CM) strains. One-year-old broodstock from each strain were separated into two size groups, with those in the large (L) group having, on average, approximately double the body weight of those in the small (S) group. Both strains exhibited a strong linear increase in absolute fecundity (slope = 58.8, p < 0.01 for CT and slope = 52.3, p < 0.01 for CM) and a slight increase in egg diameter associated with increasing female body weight (slope = 0.0002, p = 0.03 for CT and slope = 0.0003, p = 0.06 for CM). However, there were no linear correlations between female body weight and yolk-sac volume or larval body length at hatching (p > 0.05). Despite similar fecundities, the CM wild strain had larger eggs and more favourable larval properties than the CT domesticated strain (p < 0.01). However, these advantages did not result in better growth and survival of CM offspring at any stage. The CT strain showed improved growth in offspring with parents in the L group compared to those with parents in the S group across the three stages (35.7%, 50.0% and 43.9% respectively), while there was no significant increase in growth in the CM wild strain (p > 0.05). Parental body weight and strain had no effects on survival and feed conversion ratios (FCRs), with the exception that juveniles of the CM S group had the lowest SR (38.8 ± 6.0%) and FCR (1.09 ± 0.08) due to disease infection. The CT L group grew fastest and consumed the highest amount of food with similar feed efficiency to the other groups in juvenile and grow-out stages (p < 0.05). These results indicated that the pertinence of ‘the bigger the better’ paradigm varied between growth stages in the two bighead catfish strains.