Long-term growth patterns in a pond-dwelling population of crucian carp, Carassius carassius: environmental and density-related factors

Scale samples from crucian carp, Carassius carassius (L.), collected over a 10-year period from a population in an ornamental pond were used to examine patterns in growth as a function of environmental factors, including water temperatures. Back-calculated standard lengths (SL) at age differed between year classes in most cases. Annual SL increments were related to temperature and age using a non-linear growth model. Growth declined with increasing age, whereas annual SL increments increased with increasing water temperature. The best-fit model was with the total number of summer days when air temperature exceeded 20 degrees C (using water temperature equivalents of air temperature). A growth model including water temperature, age, year class, relative condition and rainfall was a better fit than other models. Year-class strength was positively correlated with water degree-days, and year-class strength negatively affected annual SL increments. The results indicate that within a strong year class of crucian carp, the growth of individual fish is reduced compared with weak year classes, suggesting that density negatively affects growth in ponds where resources are limited.