Age, growth and body condition of big-scale sand smelt Atherina boyeri Risso, 1810 inhabiting a freshwater environment: Lake Trasimeno (Italy)

The age, growth and body condition of the big-scale sand smelt (Atherina boyeri) population of Lake Trasimeno were investigated. In total, 3998 specimens were collected during the study and five age classes (from 0+ to 4+) were identified. From a subsample of 1017 specimens, there were 583 females, 411 males and 23 juveniles. The equations between total length (TL) and weight (W) were: log 10W = −2.326 + 3.139log 10TL for males and log 10W = −2.366 + 3.168log 10TL for females. There were highly significant differences between the sexes and for both sexes the value of b (slope of the log (TL-W regression) was greater than 3 (3.139 for males and 3.168 for females), indicating positive allometric growth. The parameters of the theoretical growth curve were: TLt = 10.03 cm; k = 0.18 yr-1, t0 = − 0.443 yr and Φ′ = 1.65. Monthly trends of overall condition and the gonadosomatic index (GSI) indicated that the reproductive period occurred from March to September. Analysis of back-calculated lengths indicated the occurrence of a reverse Lee’s phenomenon. This could be a symptom of predation or competition, with consequences for young specimens with slower growth and smaller size.