Artificial reproduction in 1-year-old tench (Tinca tinca L.)

Although it is generally accepted that sexual maturity of tench (Tinca tinca L.) is not reached before 2–3 years of age, a successful experiment on artificial reproduction in 1‐year‐old tench is described. It was possible to obtain semen and eggs from 48% of males and 27.7% females kept in a small concrete tank at a final density of 3 kg m⁻³ and fed on a commercial dry diet. Two hormonal treatments were applied: the first with 1354 degree‐days and the second with 2353 degree‐days. In each experiment, the positive response in males and females was around 80%. Total egg production exceeded 11% of body weight, fertilization rate was above 90% and hatching rates around 50%. These results differ little from those reported for older breeders.     

Successful gonadal development and maturation of tench (Tinca tinca L.) in small concrete ponds

The experiments were performed in a tench farm from autumn until the spawning season (June–July). Tench broodstocks from natural habitats were maintained in 25 × 6 × 1 m concrete ponds and fed on commercial trout pellets. Females and males were separated and maintained under natural photoperiod and temperature conditions at densities around 2 kg m^?2. Water flow throughout was supplied at the rate of 15 L s^?1. When females showed external signs of advanced gonadal development, induction of spawning was made by luteinizing hormone releasing factor (LH‐RH) synthetic analogue administration at three different periods of the reproductive season (June–July). A single intramuscular injection (20 μg kg^?1 body weight) was administered to 110 mature females selected from a total of 150. The females were stripped 42 h (22°C) after hormone administration. The mean rate of stripped females to the number injected was 77%. Mean relative egg weight in relation to the weight of the stripped females was 5.61%. More than 90% of the males provided semen without hormonal induction. Differences in egg production and external egg quality were observed at different times of the spawning period. It was proven that tench maintained in small concrete tanks and fed on artificial diets were able to reach gonadal maturation.     

Response of juvenile tench Tinca tinca (L.) to the anaesthetic 2-phenoxyethanol

The response of tench Tinca tinca aged 40–171 days post‐hatch (22–49 mm TL) to the anaesthetic 2‐phenoxyethanol was studied at 25°C. The lowest effective concentration of 2‐phenoxyethanol increased with age, while the highest safe concentration decreased. The fish aged 40 days post‐hatch required a significantly (P ≤ 0.05) shorter time to become anaesthetized than did older fish. The recovery time after 15 min of exposure to 2‐phenoxyethanol at 0.45 g dm^?3 was significantly shorter in the 40‐day‐old fish than in older fish. In juveniles of the same age, induction time or recovery time did not depend on their size or condition (Fulton's coefficient). At 25°C, 2‐phenoxyethanol at 0.5 g dm^?3 may be used to efficiently and safely anaesthetize T. tinca juveniles.     

Response of the tench (Tinca tinca L.) to potassium nitrate enriched water

When the tench ( Tinca tinca L.) was exposed to a slight increase, 8.5 mg/l, in the potassium content of the water, metabolic and hormonal changes occurred which lasted more than four weeks. An initial phase of lipolysis was followed by a partial consumption of glycogen reserves, which in turn was followed by a phase of gluconeogenesis. Hyperglycaemia persisted throughout the experiment. The ion distribution in erythrocytes and liver changed relatively early; there was no observable change in water content. These changes are similar to those observed during the osmoregulation of fish.     

Enhanced granulocyte phagocytosis at low winter temperature and high summer temperature in the tench (Tinca tinca L.)

Tench were captured in summer and winter when water temperature was 30 ± 3°C and 12 ± 2°C, respectively. Blood granulocytes were assayed for mobility capacity and phagocytic and microbicide capability to Candida albicans at 22°C and 30°C in summer and at 22°C and 12°C in winter. The results showed that tench granulocytes were more active in winter than in summer, and that phagocytic function was greatest at the seasonal temperature (30°C in summer and 12°C in winter) with respect to 22°C. This study suggests the importance of seasonally in the study of temperature effects on fish phagocyte function.     

The haematology of gynogenic tench, Tinca tinca L., and of recessively homozygous colour tench strains

Two wild‐coloured strains of tench (the first meiotic gynogenic generation MeiG₁, and their control diploid half siblings) and three recessively homozygous colour strains (golden, blue and alampic) were examined for the determination of basic haematological indices. The MeiG₁ strain had higher erythrocyte counts than diploid controls or the blue and alampic strains (P < 0.001), and had a higher blood haemoglobin content than all three colour strains (P < 0.001). No differences were detected among strains for haematocrit, mean corpuscular haemoglobin, or mean corpuscular volume. Both the lowest leucocyte count (P < 0.001) and leucocrit value (P < 0.001) were found in the alampic tench, and may result from a negative pleiotropic effect of this recessive homozygous genotype (bbgg). In agreement with previous findings in tench, the differential leucocyte count revealed lymphocytes to be the dominating white blood cells; their rate was about 90% in both the wild‐coloured and blue strains, and less in the other two strains (83–84%). Neutrophil granulocytes were most abundant in the MeiG₁ strain. Eosinophil granulocytes were detected only in the golden strain, and were not common (0.2%).     

A performance test with five different strains of tench (Tinca tinca L.) under controlled warm water conditions

Growth performance tests were carried out with a total of five different strains of tench (Tinca tinca L.) originating from the Czech Republic (4) and Germany (1). Tench larvae and juveniles were reared in closed recirculating systems for 446 to 452 days, respectively. At the end of each test, the tench strains showed differences in performance, e.g. specific growth rates (SGR) from 2.13 to 2.52, feed conversion ratios (FCR) from 1.75 to 3.65 kg feed per kg weight gain, and survival rates from 64.4 to 81.0%. Thus, appropriate strain selection appears to have the potential to remarkably increase productivity of the species. The highest SGR was observed in the Vodnany 96 strain in the first trial and the best FCR in the Tabor strain in the second trial. However, the rearing conditions in the recirculating systems were not optimal for tench; many fish with deformed bones (head, fins, spine) were observed in all strains, particularly in the faster‐growing strains.     

The effect of tannin concentration and egg unsticking time on the hatching success of tench Tinca tinca (L.) larvae

The influence of dose and time of eggs exposure in tannin solution on tench embryonic development, survival of embryos and percentage of larvae hatched were studied. The eggs obtained under controlled conditions from 11 tench females were fertilized with semen from 7 males and then rinsed for 1 h in Woynarovich solution (40 g urea, 30 g NaCl per 10 dm³ of water). Random samples (50 cm³) of the fertilised eggs were placed into three tannin solutions 0.05, 0.1 or 0.15% for 30, 60 or 90 s, then they were transferred to Weiss jars where incubation at 25°C took place. Tannin solution of 0.05% for 30–90 s or 0.1% for 30 s allowed effective unsticking of eggs and resulted in a very high per cent of hatched larvae. Extending the eggs rinsing time to 60 s in 0.10 and 0.15% solutions resulted in a high mortality of embryos during hatching because of hardened egg capsule.     

Determination of plasma melatonin levels by enzyme-linked immunosorbent assay (EIA) in turbot (Scophtalmus maximus L.) and tench (Tinca tinca L.)

An enzymoimmunoassay (EIA) kit for plasma melatonin (MLT) measurements was employed in tench (Tinca tinca) and in turbot (Scophtalmus maximus). Tench and turbot plasma samples were purified with a C18 reversed phase extraction columns because this kit is designed for human serum measurements. The lowest detection limit of the technique was 11.48 pg/well with a sensitivity at 50% binding of 100 pg/well. Intra-assay and inter-assay CV (%) were always less than 5% (n=8), and 9% (n=6) in tench plasma samples, and less than 5% (n=8) and 13% (n=5) in turbot plasma samples, respectively. Correlation coefficients between EIA and RIA measurements in tench and turbot plasma samples were 0.93 and 0.89 (p<0.001) respectively. Diurnal and nocturnal plasma melatonin mean levels were 14.7+/-2.1 pg/ml and 87.4+/-11 pg/ml in tench (n=15), and 3.5+/-0.4 pg/ml and 28.1+/-2.1 pg/ml in turbot (n=15). These species showed a melatonin circadian rhythm as in other animals studied. The results suggest that the commercial kit used in this experiment could be a suitable and alternative method to RIA for plasma MLT determinations in tench and turbot although it is necessary to increase volumes (1ml) and concentrate daytime samples.     

Seasonal changes in phagocytic capacity and superoxide anion production of blood phagocytes from tench (Tinca tinca,L.)

Seasonal variations in the ex vivo phagocytic function of blood cells from tench, including ingestion capacity of inert particles and its destruction (microbicide capacity) assessed by measurement of superoxide anion production, were studied. Tench were maintained under natural conditions throughout the year, and the different assays of samples taken during each season were initially performed in vitro at 22°C and the results compared. Subsequently, assays were performed at the same temperature as that of the water ponds in which the fish were kept (“seasonal temperature”: 12°C in winter, 22°C in spring and autumn and 30°C in summer) and the results compared seasonally. The results at 22°C showed that phagocytic capacity was greatest in spring and summer and lowest in winter. However, when phagocytic capacity was measured at seasonal temperature, highest values appeared in winter and lowest in summer and autumn. Nitroblue tetrazolium reduction by tench phagocytes after phagocytosing latex beads demonstrated a similar seasonal behaviour at both 22°C in each season and at seasonal temperature. The highest values appeared in summer, which suggests a better microbicide capacity in this season. The results obtained in this study suggest that for a correct interpretation of ex vivo phagocytic capacity of fish through the year it is necessary to use the same assay temperature as that of the water in which the fish is kept.     

Difference in blood and water diffusion distance in gill lamellae of diploid and triploid tench Tinca tinca (L.)

Image analysis of sagittal sections of gill lamellae of diploid and triploid tench Tinca tinca revealed the blood and water diffusion distance in diploids (2·07 μm) to be significantly higher than that of their triploid siblings (1·46 μm; P < 0·01). Lamellae of diploids compared to triploids were found to be significantly shorter (105·84 v. 132·11 μm) and thicker (18·47 v. 14·21 μm; all at P < 0·05) than those of their triploid siblings but with similar mean sectional areas (1965·44 v. 1910·86 μm²).     

Egg incubation time and hatching success in tench Tinca tinca (L.) related to the procedure of egg stickiness elimination

The experiment showed different results after a short (2 min) enzyme alcalase Merck EC 3.4.21.14 (5.0 ml L^?1 concentration) treatment of tench eggs in contrast to the traditional methods of eliminating egg stickiness involving milk solution (50 g L^?1) treatment for 70 min followed by the addition of a talc suspension (33 g L^?1) for 10 min or treatment by fine clay suspension (20 g L^?1) for 60 min or talc suspension (33 g L^?1) for 80 min. The alcalase enzyme treatment resulted in decreased egg stickiness compared with the conventional milk/clay/talc treatments, indicated by lower duration of egg incubation and higher hatching rates (anova for hatching rate, P < 0.0084). The highest hatching rate (93.2%) was achieved using the enzyme; the lowest (31.3%) was using a talc suspension (control hatching rate was 86.2%). Duration of egg incubation at degree‐days (D°) after enzyme treatment (58.6 D°) was about 4–5 h shorter than the classical method using milk solution and talc suspension (63–65 D°). Prolongation in the latter classical method may also be explained by a hardening of the egg envelopes.     

Determination of substrate preferences of tench, Tinca tinca (L.), under controlled experimental conditions

The substrate preference of tench Tinca tinca (L.), 33 2‐year‐old individuals, mean size 10 ± 0.36 cm total length, was determined using four different substrates (concrete, artificial vegetation, sand and mud) in a 26 m long maquette. The species showed a high preference (100%) for the mud. Six more trials were performed combining the substrates by pairs (concrete–vegetation, concrete–mud, concrete–sand, mud–vegetation, mud–sand, sand–vegetation). Selection order was: mud (100% of the individuals when compared with concrete and sand and 98.26 ± 2.68% when compared with artificial vegetation), artificial vegetation (100% of the individuals when compared with concrete and 99.81 ± 0.76% when compared with sand), sand (98.29 ± 3.66% when compared with concrete) and concrete.     

Plasma estradiol-17beta levels and gonadosomatic index in tench (Tinca tinca L.) reared in natural and controlled conditions

The plasma estradiol-17beta levels (E2-17beta) and gonadosomatic index (GSI) of female tench (Tinca tinca L.) reared outdoors and indoors were studied from December 1996 to April 1997. Water temperature and daylight were gradually increased (from 10 to 25 degrees C and from 9 to 16 hours per day, respectively) in the indoor group. Animals reared in natural conditions had similar plasma levels throughout the experiment but animals under controlled conditions experienced an increase in these levels in March in relation to previous months (4.81+/-0.73 ng/ml in March vs. 0.29+/-0.03 ng/ml and 0.99+/-0.31 ng/ml in January and February, respectively; P < 0.05) and in relation to animals reared outdoors (4.81+/-0.73 ng/ml vs. 0.47+/-0.19 ng/ml, respectively; P < 0.05). In April, a sharp decrease in estradiol-17beta in these animals was observed, probably associated with the end of vitellogenesis. GSI increased in both groups through the experiment and indoor animals showed greater values in March vs outdoor fishes (7.57+/-2.18 vs. 4.05+/-0.63; P < 0.05). No significant correlation was found between E2-17beta and GSI, (r = 0.35). It is concluded that manipulation of the photoperiod and temperature can modify gonadal development in tench, and this is similar to the situation in other Teleostei species. This research is the first step towards achieving, out of season, spawning in tench.     

Genetic structure and divergence of tench Tinca tinca European populations

The tench Tinca tinca is a freshwater species with human-mediated translocations, aquaculture interest and limited information on its genetic structure. mtDNA sequencing analysis of control region and two genes in 50 individuals from five European populations identified two phylogroups, with greater variability than that reported until now, and a hybridization zone in the Danube River region. Restriction analyses of additional samples reveal the complicated genetic structure characteristics of tench's wild and translocated populations, supporting future breeding practices.