Jõevähi (Astacus astacus L.) viljakus Eesti veekogudes, selle sõltumine vähi suurusest ja lapihaiguse mõju viljakusele
Laen...
Kuupäev
2012
Kättesaadav alates
ainult raamatukogus, only in library
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Käesoleva bakalaureusetöö eesmärgiks oli uurida jõevähi viljakust ja seda mõjutavaid
tegureid. Töö käigus määrati vähkide viljakus erinevates veekogudes, selgitati välja viljakuse
seos vähi pikkusega ning hinnati lapihaiguse mõju vähi viljakusele.
Jõevähi keskmine viljakus Eesti tingimustes on 198 marjatera ning see on tugevalt (r – 0,78)
seotud emasvähi pikkusega. Erinevate pikkusrühmade võrdlemisel selgus, et vähi kasvades
ühe sentimeetri võrra, suureneb keskmine viljakus ligikaudu 20%. Kõige suurematel emastel
isenditel (pikkusega 130-140 mm) oli viljakus koguni 495-651 marjatera.
Kõige viljakamad vähid olid Luguse jões (keskmine viljakus 309 marjatera) ja Vesiku ojas
(keskmine viljakus 267 marjatera). Väikseima viljakusega isendid olid Aidu tehisjärves
(keskmiselt 158 marjatera), Kuke peakraavis (keskmiselt 147 marjatera) ja Valgevälja
karjääris (keskmiselt 187 marjatera). Ilmnes ka asjaolu, et jõgedes elavad vähid on järvedes
elavatest liigikaaslastest viljakamad. Selline erinevus on ilmselt tingitud vooluveekogude
parematest keskkonnatingimustest.
Uurimustöös leidis kinnitust väide, et lapihaigus võib vähendada emasvähkide viljakust. Viie
erineva veekogu tervete ja lapihaigete vähkide võrdlemisel ilmnesid märgatavad erinevused
viljakuses enamasti vanematel ja pikematel vähkidel. Kuke peakraavi näitel on lapihaigetel
vähkidel 18% vähem marjateri kui samavanustel tervetel vähkidel. Et anda täpsem hinnang
lapihaiguse mõjust viljakusele, oleks vaja tunduvalt rohkem võrdluseks sobivaid andmeid.
Vähikasvataja jaoks on oluline, et kasvatatav populatsioon oleks võimalikult viljakas ning
haigustest vaba. Paratamatult tuleb tehistingimustes peetavat vähikarja aeg-ajalt täiendada
loodusest püütud või teistest kasvandustest hangitud vähkidega. Tuginedes uurimustöö
tulemustele, võib soovitada sugukarja täiendamiseks hankida vähke Luguse jõest ja Vesiku
ojast. Nimetatud veekogudes on jõevähi arvukus väga kõrge ning emased on üle keskmise
viljakad. Seejuures ei täheldatud ühelgi Luguse jõe ega Vesiku oja vähil lapihaiguse
esinemist, mis omab suurt tähtsust ka vähikasvatuse aspektist.
The noble crayfish is the only indigenous crayfish species in Estonia, whose survival in our nature requires more and more human intervention. Spreading crayfish plague and irresponsible human activity have caused decrease or perdition of crayfish populations in many natural water bodies. Consistent work on the recovery and replenishment of crayfish populations is supervised and financed governmentally. Knowledge of the fecundity of crayfish and of the influencing factors will conduce to the restocking and creating new and vital populations. Nature-field legislation and wide-range information, rational management of crayfish stock and progress of the technology of crayfish farming are largely based on scientific research. The subject of this study is important from the perspective of the development of crayfish farming and from the perspective of increasing the economical importance of natural crayfish stock. The aim of this study is to provide an overview of crayfish biology and also to study the fecundity of crayfish and the factors that influence the latter. First task of this study was to determine the fecundity of noble crayfish in different water bodies. Second task was to analyze how the fecundity is related to the length of crayfish. Third task was to estimate the effect of the burn spot disease on the fecundity of crayfish. This study also aims to contribute to the technology of crayfish farming, therefore it is important to enable the practical use of the results. For example, which water bodies are most suitable for the replenishment of crayfish brood-stock The material for this study was collected in 2000–2011, when 605 crayfish were analyzed. The analyzed crayfish were caught from twelve different water bodies (lakes Nõuni, Pangodi 45 and Tänavjärv, artificial lakes Aidu and Valgevälja, rivers Jõksi, Kuke, Luguse, Riksu, Soodla, Vesiku and Ärma. The fecundity of crayfish was determined by analyzing the crayfish preserved in the freezer. The defrosted crayfish were grouped according to the water bodies of their origin and these groups were analyzed separately. Before determining the fecundity the crayfish were measured (extra 1). The occurence of burn spot disease was also determined via visual examination (spots will be clearly visible after boiling) (extra 2). Absolute fecundity was measured as a number of ripe ovocytes in ovary. Before counting, crayfish were boiled. The results of this study show that average fecundity in Estonia is 198 eggs and that it depends strongly (r – 0,78) on total lenght of crayfish. Comparing of different length-groups showed that when crayfish length increases by 1 cm, then average fecundity increases approximately by 20%. The fecundity was highest in rivers Luguse (average 390 eggs) and Vesiku (average 267 eggs). Lowest fecundity was determined amongst crayfish caught from artificial lakes Aidu (average 158 eggs) and Valgevälja (average 187 eggs) and river Kuke (average 147 eggs). It appears that crayfish living in rivers are more fecund than those living in lakes. The reason for this is apparently the better environmental conditions in flowing water.female crayfish. The differences in fecundity occur mostly amongst older and longer crayfish. The example of river Kuke shows that the diseased individuals have 18% less eggs than their healthy companions of same age. More specific data is required for further conclusions. It is important for crayfish farmers that the population is as fecund and as free of diseases as possible. Crayfish population kept in artifical conditions need a renewal from time to time to avoid inbreeding and to replace dead individuals. The results of this study suggest that it is best to replace dead broodstock with crayfish caught from rivers Luguse and Vesiku. The crayfish population in these rivers is largest and most fecund. Also no burn spot disease was discovered amongst crayfish caught from these rivers, but that does not exclude the possible presence of pathogens there.
The noble crayfish is the only indigenous crayfish species in Estonia, whose survival in our nature requires more and more human intervention. Spreading crayfish plague and irresponsible human activity have caused decrease or perdition of crayfish populations in many natural water bodies. Consistent work on the recovery and replenishment of crayfish populations is supervised and financed governmentally. Knowledge of the fecundity of crayfish and of the influencing factors will conduce to the restocking and creating new and vital populations. Nature-field legislation and wide-range information, rational management of crayfish stock and progress of the technology of crayfish farming are largely based on scientific research. The subject of this study is important from the perspective of the development of crayfish farming and from the perspective of increasing the economical importance of natural crayfish stock. The aim of this study is to provide an overview of crayfish biology and also to study the fecundity of crayfish and the factors that influence the latter. First task of this study was to determine the fecundity of noble crayfish in different water bodies. Second task was to analyze how the fecundity is related to the length of crayfish. Third task was to estimate the effect of the burn spot disease on the fecundity of crayfish. This study also aims to contribute to the technology of crayfish farming, therefore it is important to enable the practical use of the results. For example, which water bodies are most suitable for the replenishment of crayfish brood-stock The material for this study was collected in 2000–2011, when 605 crayfish were analyzed. The analyzed crayfish were caught from twelve different water bodies (lakes Nõuni, Pangodi 45 and Tänavjärv, artificial lakes Aidu and Valgevälja, rivers Jõksi, Kuke, Luguse, Riksu, Soodla, Vesiku and Ärma. The fecundity of crayfish was determined by analyzing the crayfish preserved in the freezer. The defrosted crayfish were grouped according to the water bodies of their origin and these groups were analyzed separately. Before determining the fecundity the crayfish were measured (extra 1). The occurence of burn spot disease was also determined via visual examination (spots will be clearly visible after boiling) (extra 2). Absolute fecundity was measured as a number of ripe ovocytes in ovary. Before counting, crayfish were boiled. The results of this study show that average fecundity in Estonia is 198 eggs and that it depends strongly (r – 0,78) on total lenght of crayfish. Comparing of different length-groups showed that when crayfish length increases by 1 cm, then average fecundity increases approximately by 20%. The fecundity was highest in rivers Luguse (average 390 eggs) and Vesiku (average 267 eggs). Lowest fecundity was determined amongst crayfish caught from artificial lakes Aidu (average 158 eggs) and Valgevälja (average 187 eggs) and river Kuke (average 147 eggs). It appears that crayfish living in rivers are more fecund than those living in lakes. The reason for this is apparently the better environmental conditions in flowing water.female crayfish. The differences in fecundity occur mostly amongst older and longer crayfish. The example of river Kuke shows that the diseased individuals have 18% less eggs than their healthy companions of same age. More specific data is required for further conclusions. It is important for crayfish farmers that the population is as fecund and as free of diseases as possible. Crayfish population kept in artifical conditions need a renewal from time to time to avoid inbreeding and to replace dead individuals. The results of this study suggest that it is best to replace dead broodstock with crayfish caught from rivers Luguse and Vesiku. The crayfish population in these rivers is largest and most fecund. Also no burn spot disease was discovered amongst crayfish caught from these rivers, but that does not exclude the possible presence of pathogens there.
Kirjeldus
Märksõnad
jõevähk, paljunemine, loomahaigused, arvukus, vähikasvatus, veekogud, Eesti, bakalaureusetööd