Fevzi Yilmaz

Reproductive biology of the tench Tinca tinca (L., 1758) inhabiting Porsuk Dam Lake (Kutahya, Turkey)

Maturity age, spawning time and fecundity of tench in Porsuk Dam Lake were determined. Field and laboratory studies show that males and females become sexually mature at age 3 and 4, respectively, and the spawning period extends from late April to the beginning of July. The number of eggs ranged from 13,766 to 43,148 and the highest value of GSI for the species is in June, while the lowest value (nearly zero) is in July.

Natural and anthropogenic factors affecting the nest-site selection of Loggerhead Turtles, Caretta caretta, on Dalaman-Sarıgerme beach in South-west Turkey.

Abstract The nesting activities of Loggerhead Turtles (Caretta caretta Stejneger, 1902) and anthropogenic factors affecting them were monitored over 7 years (2002–2008) on Dalaman-Sarıgerme beach, one of the main nesting grounds in Turkey. Out of the 2620 nesting emergences recorded during the entire study period, only 645 (24.6%) resulted in successful nesting, giving an annual mean number of nests of 92. The collective number of eggs in these nests numbered 50239, with 40079 (79.8%) of them producing hatchlings. Out of the total number of eggs laid, 8128 (16.2%) resulted in dead embryos and 2032 (4.0%) in unfertilized eggs. The mean incubation period averaged 49 days (range 40–67 days) and the mean clutch size was 79.0 (range 18–150 eggs). Turtle nests were more concentrated on the undeveloped parts of the beach than on developed parts. In the other sections, few emergences occurred and either no or few nests were recorded. In Section I, which contained hotels and water sports facilities, only a few non-nesting emergences were observed. Of the number of nests that were observed, 32% were laid in Section II, which contained recently built hotels, 60% were in Section III and 8% were in Section IV, the undeveloped portion containing beach rocks. There is very clear evidence that the Loggerhead Turtles are shifting their nesting sites to the undisturbed sites along the beach. The negative factors that seem to be affecting them include water sports, hotel lights and beach rocks. In order to protect sea turtles, there needs to be a better understanding of how effective beach protection can be established.

Feeding habits of the Thin-lipped Grey Mullet, Liza ramada, in Gökova Bay in the southern Aegean Sea

Abstract We analysed the stomach contents of 240 Thin-lipped Grey Mullets, Liza ramada, in Gökova Bay in the southern Aegean Sea, to study their feeding habits. The diet comprised species belonging to 32 genera, with 25 of them belonging to plants and 7 to animals. The diet consisted of 97.41% of Bacillariophyta, 0.24% of Chlorophyta, 0.16% of Cyanophyta and 2.17% animal organisms.

Differences in metal profiles revealed by native mussels and artificial mussels in Sarıçay Stream, Turkey: implications for pollution monitoring

Using the native mussel Unio crassus and artificial mussels (AMs), profiles of 11 metals (Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, U, Zn) were determined and compared in winter and summer along a pollution gradient in Saricay Stream, Turkey. Principal components analysis and correlation analysis showed that metal profiles in the native mussels and AMs were different. Concentrations of most metals were significantly higher in the native mussels compared with AMs, suggesting that metals in Saricay Stream predominantly existed in suspended particulates and food compartments, rather than in dissolved form. Although U was not readily accumulated by the native mussels, it could be taken up by AMs. Overall, the results suggest that the use of native mussels and AMs in water quality monitoring can provide complementary information and a better estimate and coverage of different metal species and forms in aquatic environments.

Metal Accumulations in Water, Sediment, Crab (Callinectes sapidus) and Two Fish Species (Mugil cephalus and Anguilla anguilla) from the Köyceğiz Lagoon System–Turkey: An Index Analysis Approach

The concentrations of six metals (Hg, Cd, Cu, Pb, Cr and Zn) individual total metal load (IMBI) values and its relation to condition index were determined in water, sediment and tissues of crab (Callinectes sapidus) and two fish species (Mugil cephalus and Anguilla anguilla) inhabiting Köyceğiz Lagoon System. The average distribution of the IMBI values ranged from 0.033 to 0.265. Distribution patterns of IMBI in species follow the sequence: A. anguilla > M. cephalus > C. sapidus. Results showed that there are positive relationships between species sizes and metal levels in most cases. The concentrations of Pb in muscle in the three studied species were in all cases considerably higher than the maximum levels set by law. Average Cd, Cu and Zn values in M. cephalus were also higher than the limits proposed for fish by FAO/WHO, EC and TFC. Therefore, the human consumption of all analysed species is not recommended.

Seasonal and age-related changes in semen characteristics and composition of seminal plasma in sex-reverse female rainbow trout (Oncorhynchus mykiss) in comparison with normal males

All-male or all-female progeny is preferable in reproduction of fish species. In rainbow trout, all-female progeny is desirable, and the most common and healthful approach is to use sex reversed (SR) females as broodstock by including androgen hormones through the diet at the larval stage. The purpose of this study was to determine the differences and changes of seminal plasma ions (Na+, K+, Ca2+, Mg2+ and Cl-) and pH in 2 to 3 and 3 to 4 year-old SR females, compared with 2 to 3 year-old normal (N) males at the beginning, middle, and end of the spawning season (SS). Additionally, osmolality, spermatozoa concentration, and sperm motility characteristics were determined. Percentages of sperm motility of SR females were negatively correlated with seminal plasma pH and sperm concentrations (r = -0.479 and r = -0.534, respectively, P < 0.05). Seminal plasma pH (7.14 ± 0.05 to 7.40 ± 0.10) in SR females was less than for N males (7.66 ± 0.10 to 8.04 ± 0.10) at all periods of the SS (P < 0.05). The Ca2+ concentrations in the mid-SS were 0.74 ± 0.23 mM in N males, 1.09 ± 0.29 mM in 2 to 3 year-old SR females, and 0.83 ± 0.29 in 2 to 3 year-old SR females, without significant differences (P > 0.05). Furthermore, using of 2 to 3 year-old rather than 3 to 4 year-old SR females for reproduction could provide an advantage in terms of sperm motility characteristics. These findings could be useful for not only understanding of SR of semen from sexually reversed females but also for design of a maturation medium both for further studies and aquaculture production.