The growth and reproduction of white bream (Blicca bjoerkna L. 1758) in an oligo-mesotrophic lake in northwest Anatolia (Sapanca, Turkey)

Growth parameters and the reproduction period of white bream (Blicca bjoerkna L. 1758) sampled from Sapanca Lake were determined monthly between November 2000 and October 2001. Three hundred and fifty white bream specimens caught ranged in age from 1(+) to 9(+) years, and the majority of the samples consisted of individuals of the 5(+)-year-old age group. The von Bertalanffy equation was determined as Lt = 22.169 (1 - exp {-0.215[t + 0.986]}), empty set: 2.02 for males and Lt = 31.917 (1 - exp {-0.122[t + 1.087]}), empty set': 2.10 for females. The length-weight relationship was estimated as W = 0.0046 TL exp. 3.315 +/- 0.002 for males (r(2) = 0.9653, P < 0.05), and W = 0.0036 TL exp. 3.417 +/- 0.002 for females (r(2)= 0.9671, P < 0.05). Regression coefficients for sex were significant (t-test, P < 0.05). The slope (b) significantly differed (ANCOVA, P < 0.05) between months. The fact that the b values for male and female white breams differed from 3.0 indicates that there was positive allometric growth. Sex ratio was 1:1.36 (chi(2); P < 0.05). Spawning period of white breams began at the end of April and continued until the beginning of July; water temperature during this period ranged between 13.7 and 28.5 degrees C

Feeding ecology of vimba (Vimba vimba L., 1758) in terms of size groups and seasons in Lake Sapanca, northwestern Anatolia

The seasonal changes of diet in the guts of 298 vimbas (Vimba vimba L.) caught on a monthly basis in Lake Sapanca from August 2003 to July 2004 were analyzed. V vimba fed on ostracods, gastropods, Dreissena polymorpha (mollusks), fish larvae, macrophytes, oligochaetes, chironomids, phytoplankton, and detritus. The gut fullness index (GFI) indicated that vimbas increased their feeding activity in summer and decreased it in winter. The correlation between GFI and temperature was significant (0.839, P < 0.01). The water temperature shift was one of the critical environmental factors affecting the feeding of vimbas in Lake Sapanca. The lowest similarity of diet composition was between the juvenile vimbas in autumn and the adult vimbas in spring (cluster analysis), while the highest similarity of diet composition was between adult individuals in autumn and winter (cluster analysis). In both size groups and in all seasons, the main food items were macrophytes, D. polymorpha, and phytoplankton (particularly bacillariophytes). Of animal food items, adult individuals fed mostly on D. polymorpha, while ostracods were consumed only by juvenile fish in spring, summer, and autumn. The benthic-omnivorous strategy of vimba is demonstrated by the high abundance of plant foods in their guts, confirming this mixed type of diet

Feeding ecology of vimba (Vimba vimba L., 1758) in terms of size groups and seasons in Lake Sapanca, northwestern Anatolia

The seasonal changes of diet in the guts of 298 vimbas (Vimba vimba L.) caught on a monthly basis in Lake Sapanca from August 2003 to July 2004 were analyzed. V. vimba fed on ostracods, gastropods, Dreissena polymorpha (mollusks), fish larvae, macrophytes, oligochaetes, chironomids, phytoplankton, and detritus. The gut fullness index (GFI) indicated that vimbas increased their feeding activity in summer and decreased it in winter. The correlation between GFI and temperature was significant (0.839, P &lt; 0.01). The water temperature shift was one of the critical environmental factors affecting the feeding of vimbas in Lake Sapanca. The lowest similarity of diet composition was between the juvenile vimbas in autumn and the adult vimbas in spring (cluster analysis), while the highest similarity of diet composition was between adult individuals in autumn and winter (cluster analysis). In both size groups and in all seasons, the main food items were macrophytes, D. polymorpha, and phytoplankton (particularly bacillariophytes). Of animal food items, adult individuals fed mostly on D. polymorpha, while ostracods were consumed only by juvenile fish in spring, summer, and autumn. The benthic-omnivorous strategy of vimba is demonstrated by the high abundance of plant foods in their guts, confirming this mixed type of diet