Morphological changes of silver and bighead carp in the Yangtze River over the past 50 years.

Multivariate analysis was adopted to analyze 30 morphometrical characteristics of 121 one-year-old juvenile silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) bred during the 1950s ("the former population") and 2008 ("the current population") and collected from the middle reach of the Yangtze River. The average discriminant accuracies of the former and current silver and bighead carp population were 94.2% and 98.0%, respectively. Discriminant analysis also revealed that significant differences in morphology occurred between the former and current populations of both carp in overall characteristics. One-way analysis of variance indicated that between former and current populations, silver carp showed highly significant differences (P<0.01) in twelve of their characteristics and significant differences (P<0.05) in eight of their characteristics, while bighead carp showed highly significant differences (P<0.01) in eight of their characteristics and significant differences (P<0.05) in eight of their characteristics. Six head morphology variables of the current silver and bighead carp were significantly or highly significantly larger than the former populations; fourteen characteristics of silver carp and ten characteristics of bighead carp of the current populations, mainly reflecting truck and tail morphology, were significantly or very significantly smaller than the former populations. Our results indicate that silver and bighead carp have developed a larger head and smaller truck and tail during the last 50 years. Due to such morphological changes, it seems apparent that the heads of these fish species need to be considered in regards to human diets, particularly in relation to economic and nutritious value.