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Influence of age and rearing conditions of a fish on the chance to survive in the wild
Lyach, Roman ; Frouzová, Jaroslava (advisor) ; Čech, Martin (referee)
The task of this thesis is to summarize all the most important biotic and abiotic factors that can influence chances of reared fish to survive in the wild. It contains some of the most frequently reared and popular fishes, such as Sander lucioperca (pike perch), Samo trutta (trout), Micropterus salmoides (largemouth bass), Esox lucius (northern pike), Esox masquinongy (muskellunge) and the hybrid of northern pike and muskellunge, the tiger muskellunge. Mainly the factors such as success, survival, rate of growth and mortality have been studied. Survival increases with the size of the fish because of the fact that larger fish can easily avoid predation. Pellet-reared fish show higher mortality than minnow-reared fish because of the loss due to predation and also slightly worse ability to catch living prey and obtain food, even though their diet contains similar species. Temperature can also affect the mortality of the stocked fish, mainly when the temperature difference between the rearing pond or hatchery and the new environment exceeds 10 řC, which brings loss of majority of the stocked fish. It has been revealed that genetics is very important during the process of stocking, while fish from the local population show better abilities to adapt to the environment than those from other geographic...
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Diet of Eurasian otter (Lutra lutra) in relation to the stocking of brown trout (Salmo trutta m. fario) and grayling (Thymallus thymallus)
Lyach, Roman ; Čech, Martin (advisor) ; Poledník, Lukáš (referee)
This study aimed to evaluate otter predation on stocked trout and grayling. The diet composition of piscivorous Eurasian otters (Lutra lutra) was studied on the stream Chotýšanka in central Bohemia using spraint (otter faeces) analysis during one winter period (90 days). Stocking took place mostly in the second half of 2005. Around 5000 hatchery-reared brown trouts (Salmo trutta m. fario) of size about 10 cm, 600 graylings (Thymallus thymallus) of the same size and 480 rainbow trouts (Oncorhynchus mykiss) of size about 30 cm were stocked into the stream. Spraints were collected in December 2005 and January 2006. We found and identified 1531 fish in the spraints. The primary food source of otters was fish (almost 85 % of biomass). The main fish prey was small - sized, below 20 g in weight and 13 cm in length. The bulk of otter's diet consisted of less - valued species, especially the gudgeon (Gobio gobio). Other frequently consumed fish species were the European chub (Squalius cephalus), the common carp (Cyprinus carpio), the European perch (Perca fluviatilis), the brown trout and the rainbow trout. Consumption of stocked brown trout was 1,80 %, while cosumption of stocked rainbow trout was 10,90 % of biomass. Otters in this area consumed about 723 - 1446 brown trouts and 72 - 144 rainbow trouts...
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The role of fish-eating predators and socio-economic trends in recreational fishing
Lyach, Roman ; Čech, Martin (advisor) ; Adámek, Zdeněk (referee) ; Jurajda, Pavel (referee)
Recreational fishing is a very important leisure activity and one of the most important ways how humans influence freshwater habitats and wild fish populations. Both fish-eating predators and socio-economic trends play a major role in recreational fishing. This thesis found that the Eurasian otter feeds mainly of small (5-10 g) and very abundant fish species of low angling value. In this case, gudgeon Gobio gobio dominated in the otter diet. The overlap between catches of otters and anglers was very low, and commercially important salmonids made up only 10 % of the otter diet by biomass. Cormorants also prey mostly on smaller (10-100 g) a very abundant fish species. In this case, roach Rutilus rutilus dominated in the cormorant diet. The overlap between catches of cormorants and anglers was also quite low. Commercially important fish species made up less than 10 % of the cormorant diet. Even though cormorants consume mostly smaller fish, they are potentially removing fish that serve as prey for piscivores, and they are also removing smaller fish that would grow into angling size. The Atlantic salmon Salmo salar reintroduction programme has not yet been successful. However, cormorant predation is not the main reason for its low success. The main problem is somewhere on the lower River Elbe in...
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Diet of Eurasian otter (Lutra lutra) in relation to the stocking of brown trout (Salmo trutta m. fario) and grayling (Thymallus thymallus)
Lyach, Roman ; Čech, Martin (advisor) ; Poledník, Lukáš (referee)
This study aimed to evaluate otter predation on stocked trout and grayling. The diet composition of piscivorous Eurasian otters (Lutra lutra) was studied on the stream Chotýšanka in central Bohemia using spraint (otter faeces) analysis during one winter period (90 days). Stocking took place mostly in the second half of 2005. Around 5000 hatchery-reared brown trouts (Salmo trutta m. fario) of size about 10 cm, 600 graylings (Thymallus thymallus) of the same size and 480 rainbow trouts (Oncorhynchus mykiss) of size about 30 cm were stocked into the stream. Spraints were collected in December 2005 and January 2006. We found and identified 1531 fish in the spraints. The primary food source of otters was fish (almost 85 % of biomass). The main fish prey was small - sized, below 20 g in weight and 13 cm in length. The bulk of otter's diet consisted of less - valued species, especially the gudgeon (Gobio gobio). Other frequently consumed fish species were the European chub (Squalius cephalus), the common carp (Cyprinus carpio), the European perch (Perca fluviatilis), the brown trout and the rainbow trout. Consumption of stocked brown trout was 1,80 %, while cosumption of stocked rainbow trout was 10,90 % of biomass. Otters in this area consumed about 723 - 1446 brown trouts and 72 - 144 rainbow trouts...
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Influence of age and rearing conditions of a fish on the chance to survive in the wild
Lyach, Roman ; Frouzová, Jaroslava (advisor) ; Čech, Martin (referee)
The task of this thesis is to summarize all the most important biotic and abiotic factors that can influence chances of reared fish to survive in the wild. It contains some of the most frequently reared and popular fishes, such as Sander lucioperca (pike perch), Samo trutta (trout), Micropterus salmoides (largemouth bass), Esox lucius (northern pike), Esox masquinongy (muskellunge) and the hybrid of northern pike and muskellunge, the tiger muskellunge. Mainly the factors such as success, survival, rate of growth and mortality have been studied. Survival increases with the size of the fish because of the fact that larger fish can easily avoid predation. Pellet-reared fish show higher mortality than minnow-reared fish because of the loss due to predation and also slightly worse ability to catch living prey and obtain food, even though their diet contains similar species. Temperature can also affect the mortality of the stocked fish, mainly when the temperature difference between the rearing pond or hatchery and the new environment exceeds 10 řC, which brings loss of majority of the stocked fish. It has been revealed that genetics is very important during the process of stocking, while fish from the local population show better abilities to adapt to the environment than those from other geographic...
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