The roach, Rutilus rutilus, is a Cyprinid which is widely distributed throughout freshwater systems in Europe. It is one of the most abundant and important commercial fish species in Greece. Age, growth, reproduction and fecundity of roach were studied in Lake Volvi from 1997-1998 females had higher growth in length (L∞=277.18 mm, k=0.097) than adult males (L∞=185.60 mm, k=0.148). All males older than one year and larger than 70 mm, and all females older than two years and larger than 80 mm were sexually mature. The breeding period spanned from the end of March till mid April. Fecundity ranged from 2,036 to 31,653 eggs (mean 8,102 eggs) and relative fecundity from 76.06 to 333.94 eggs/g (mean 186.78 eggs/g). Diameter of eggs were 1.3 ± 0.07 mm and weighted 0.0011 ± 0.0002 g . The weight of eggs were independent of length and age of individuals (P>0.05), however, there was a significant relationship between weight and egg diameter (P<0.05). Absolute fecundity depended on length, weight and age of the females. The relationship between absolute fecundity and length were less obvious in the case of relative fecundity and egg size. Estimated growth was at the lower end when compared with other studies conducted elsewhere.

Length-weight relations (LWRs) and different indices of condition factor for roach from Lake Volvi (Northern Greece) were estimated. Results showed that roach are heavier of a given length in Lake Volvi than in other areas worldwide, with females exhibited higher weight than males of the same length. Significant differences (P<0.05) of LWRs were also exhibited between sexes depending on month. CLARK condition factor peaked at the end of summer displaying no significant difference between sexes, whereas the other three estimated condition factors (Allometric, FULTON, LE CREN) peaked in winter. The estimation of different proxies of condition factor disaggregated by sex might reduce the uncertainty raised by the estimation of fish growth.

This study evaluated the effects of different dietary protein levels on growth performance and nutrient utilization of snarpsnout sea bream (Diplodus puntazzo) juveniles. Five isoenergetic diets were formulated to contain a dietary protein level at 30% (P30), 35% (P35), 40% (P40), 45% (P45) and 50% (P50). Each diet was randomly assigned to triplicate groups of fish (IBW 2.80 g) and fed to apparent satiation for 100 days. The dietary protein to energy ratio significantly affected the feed intake with the lower ratios leading to a higher feed consumption. The growth performance of D. puntazzo was gradually increased as the dietary protein level increased up to 40% and then gradually reduced as the dietary protein increased further to 45% and 50%. The feed efficiency got improved as dietary protein levels increased up to 45% but slightly decreased at 50% protein level. A second-degree polynomial regression analysis estimated that a dietary protein level at 41.4% and 43.8% delivered the maximum weight gain and the higher feed efficiency, respectively. The increased dietary carbohydrate and lipid levels in fish fed a low protein diet (P30) resulted in a significant deterioration of feed conversion and growth rates showing also reduced nutrient retentions and causing severe mortalities.