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Vliv hustoty obsádek sumečka afrického (Clarias gariepinus) na efektivitu jeho intenzivního chovu v recirkulačním akvakulturním systému
TRNKA, Kamil
This study is a dressing the breeding process of the african catfish kept in RAS recycling waste heat from the biogas plant. The weight, SGR, FCR, FC, survival rate and were evaluated. During the first test different breeding densities were established (30, 60, 90, 120 kg.m-3) and fishes were kept in the tanks without lowering the the density to the original. Into the tanks with the same quality of the water, we introduced juveniles of the african catfish. Results of the first test showed that the best growth of the african catfish is achieved in the breeding density up to 230 kg.m-3. In the second experiment, the different breeding densities were established (90, 120, 150 a 180 kg.m-3). These densities were periodically lowered to the starting density each Month. In this test we achieved higher SGR and lower FCR. There were no significant differences among the density's groups. Third test was based on the presence of the sorting of the fish in tanks. While not sorting negative influence has appeared. In the non-sorted group, we found couple of marked-sized fish and couple of bellow average fish. Also, the growth parameters showed better results in the sorted group. All experiments showed that the best breeding density is from 180 up to 230 kg.m-3.
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Vliv teploty vody a intenzity světla na raný vývoj sumečka afrického v komerčním chovu
PROKEŠOVÁ, Markéta
The successful production of quality early fish stages is crucial for artificial rearing fish species. Nevertheless, it is quite a problematic process, because fish as poikilothermic organisms are highly sensitive to various environmental conditions. Moreover, both fish embryos and larvae are more affected by biotic and abiotic factors (such as predation, stocking density, temperature, light, pH, salinity, oxygen saturation, feeding availability, or their interactions) than older juveniles or adults. Most fish processes such as reproduction, metabolism, survival, development and growth can be considerably (positively, negatively or not) influenced by these conditions. Therefore, it is important to understand their impacts on fish stages during embryonic, larval, juvenile, adult, and eventually the senescent period. Then, following the application of new knowledge to the practise, especially species- and age-specific optimal conditions, should result in higher survival, better growth rate, well developed fish without deformities and lower cannibalism. The objectives of the present thesis were to assess the effect of water temperature and light intensity on the early development (embryonic and larval period) of African sharptooth catfish as a perspective fish species for freshwater intensive aquaculture. Due to its great characteristics (for instance fast growth, ability to breathe atmospheric air, rearing at high stocking density) this species can meaningfully contribute to the global aquaculture production which is expected to rise in the coming years. However, there are still some difficulties in the early rearing African sharptooth catfish regarding the cannibalism, feeding, survival and necessity of detailed information about the effects of some abiotic factors and their interactions.
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The effect of water temperature on early ontogeny in African catfish (Clarias gariepinus)during post - embryonic development
FRANTA, Pavel
This theses is made up from two methodologically identical experiments, which involved observing the starting time of key sections of early ontogeny (H95, S95, Re95) at a temperature of 24°C. The experiments used 29 groups of eleuterembryoes/larvae which were fed for 30 days, but timing of initial feeding of exogenous food was different between the groups. The first group began initial feeding at the age 72 hPF and every other group was fed for the first time 6 hours later than the previous group (the last group was fed at the first time at the age 240 hPF). The group, which wasn´t fed exogenous food during the experiment, served as control. The effect of timing of start feeding on morphometric and gravimetric characteristics, size distribution, survival and rate of cannibalism in eleuterembryoes/larvae was examined. A temperature of 24 °C was determined the hatching time of eleuterembryoes after 36, resp. 33 hours (1st, respectively 2nd experiment) from fertilization. The start of intake of exogenous food (S95) was determined at age 123 hPF, yolk sac absorption at age 150 hPF during the 1st experiment. At the 2nd experiment the start of intake exogenous food was determined at age 115 hPF and yolk sac absorption at age 161 hPF. During the interval from H95 to S95 records showed an increased rate of growth, especially the caudal part of the body. At the age from S95 to Re95, growth of unfed larvae was stopped (first effect of starvation). Almost all monitored parametres were significantly affected (P < 0,01) by timing of start feeding except for rate of cannibalism. While the percentage representation of large sized and medium sized individuals (the potential cannibals) was decreased with increasing the time of start feeding, the rate of cannibalism wasn´t changed. However the number of small sized individuals was increased with increasing the time of start feeding. The study of the African catfish confirmed the negative impact on survival, which is caused by a delay in initial feeding. Unlike survival, with morphometric parametres there wasn´t observed a significant decrease in values, provide the larvae was first fed before reaching the age of 216 hPF. It was also found that almost 100 % of the individuals in the control (unfed) group died at age 377 hPF. However the first indications of increasing mortality was observed in age 283 hPF. Based on the above information, the PNR (point of no return) was reached approximately at the age of 270 hPF in African catfish
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Effect of water temperature on early life history in African catfish (Clarias gariepinus)
PROKEŠOVÁ, Markéta
In the present M. Sc. thesis the effect of water temperature (thermal range: 17.4 - 38.6 °C) on early life history (during interval from egg fertilization to full yolk sac depletion by 50 % of larvae; Fe - Re50) in African catfish (Clarias gariepinus) was examined. Length of the incubation period (i. e. interval from egg fertilization to the moment of hatching of 50 % of individuals; Fe - H50), length of the hatching period (i. e. interval from hatching of 5 % of individuals to hatching of 95 % of individuals; H5 - H95), length of the period up to the first intake of exogenous food (i. e. interval from H50 to the first intake of exogenous food by 50 % of individuals; H50 - S50) and length of the period up to the full yolk sac resorption (H50 - Re50) were inversely proportional to the incubation temperature. Period of the yolk sac resorption was significantly prolonged (approximately six times) because of using of exogenous food (compared to treatments without added external food supplies). Embryonic development was theoretically stopped at temperature 15.4 °C and hatching occured after c. 12 effective day-degrees. Size of larvae increased during embryonic and larval period. Size of larvae at H50, S50 and Re50, was inversely proportional dependent on the incubation temperature. Size of individuals at Re50 was increased (approximately twice) because of using of exogenous food (compared to treatments without added external food supplies). Yolk sac volume (YsV) decreased during embryonic and larval period. YsV at H50 was correlated with size of egg and YsV was S50 was inversely proportional to the incubation temperature. A dry weight of yolk sac at H50 represented c. 89 % of total dry weight of hatched larvae. During the period of endogenous feeding c. 75 % of dry weight of egg was converted into the larval somatic tissues. Efficiency of energy conversion during the period of endogenous feeding is lower (60 %). The energetical value of total dry matter and content of sulfur in dry matter was decreasing during the period of endogenous feeding (in order: egg, hatched larvae, larvae at Re50). Content of nitrogen and carbon in dry matter was increasing during the embryonic period and afterwards was decreasing during the larval period. In term of survival, the zone of thermal tolerance for early life history in African catfish ranges from 19 to 33 °C (with thermal optimum between 23 and 30 °C), i. e. this fish belongs to the typical thermophilous species. The suboptimal temperatures lies within intervals 21 - 23 °C and 30 - 33 °C, respectively. Temperatures below 17.5 °C as well above 35.5 °C can be considered as the lethal temperatures already during embryonic period and those below 19 °C and above 33 °C as the lethal ones during larval period, respectively. In term of bioenergy, the thermal optimum for early life history in African catfish lies between 23 - 28 °C.
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