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Mortalidade de ovos de sardinha e carapau por parasitismo, impacto na sobrevivência das fases iniciais de vida e implicações para a gestão destes recursos
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Resumo(s)
A sardinha (Sardina pilchardus) e o carapau (Trachurus trachurus) são duas espécies com uma enorme
importância ao nível das cadeias tróficas marinhas e com um elevado valor comercial, apresentando
uma peculiar importância na Península Ibérica, onde fazem parte da alimentação tradicional portuguesa.
As populações de sardinha e carapau apresentam flutuações nos seus mananciais, não sendo a origem
destas totalmente conhecida. Uma das causas conhecidas para a mortalidade na fase inicial de vida (ovo)
é o parasitismo por Ichthyodinium chabelardi, um endoparasita de ovos de peixes pelágicos, como a
sardinha e o carapau, que acaba, em todos os casos conhecidos, por levar o seu hospedeiro à morte.
Este trabalho teve dois objetivos principais: (i) estudar a prevalência da infeção por Ichthyodinium
chabelardi em ovos de sardinha e carapau; (ii) analisar a distribuição espacial dos ovos infetados na área
de estudo (costa sul e oeste das águas Ibéricas atlânticas), tendo em conta determinados fatores
ambientais. Desta forma, procedeu-se à análise de amostras de ictioplâncton, de 10 campanhas (em 7
destas foram analisados ovos de sardinha e em 5 de carapau), classificando os ovos por estádios de
desenvolvimento e níveis de infeção. Um objetivo complementar considerou a análise do possível
mecanismo de infeção dos ovos pelo parasita. Para este fim, foi explorada a hipótese de infeção na fase
adulta (antes da emissão dos oócitos) e desenvolvidos protocolos de análise molecular para a deteção
do parasita em gónadas de sardinha. Os resultados mostraram que a percentagem de ovos infetados pelo parasita (prevalência) nos anos analisados variou entre 0,80% e 4,32% nos ovos de sardinha e entre 0,82% e 10,97% nos ovos de carapau e que a percentagem de estações com ovos parasitados (PEOP) variou entre 2,53% e 15,32% no caso dos ovos de sardinha e entre 2,00% e 12,59% no caso dos ovos de carapau. Foi possível identificar a profundidade como um possível fator ambiental responsável para estas flutuações, bem como a localização geográfica (costa ocidental vs costa sul) e a temperatura (esta última apenas para a sardinha) através de análises GLM efetuadas, em que se tomaram determinados fatores ambientais como variáveis independentes e o número de ovos parasitados como variável dependente. Quando se comparou a mortalidade total dos ovos de sardinha com a prevalência de infeção nos mesmos anos, foi possível verificar que os anos com maior percentagem de mortalidade total foram também os anos com maior prevalência de infeção pelo parasita. Os resultados relativos à análise molecular, que indiciaram a presença de fragmentos de ADN de Ichthyodinium chabelardi nas gónadas de sardinha, parecem indicar que parte do ciclo de vida do
parasita ocorre na fase adulta do hospedeiro, pelo que os oócitos, quando expelidos pelas fêmeas,
poderão já estar contaminados pelo parasita em questão, carecendo, no entanto, esta informação de
confirmação pela sequenciação dos fragmentos de ADN que se pensam ser do parasita. Torna-se evidente, assim, a importância de conhecer melhor o ciclo de vida de Ichthyodinium chabelardi e de aprofundar a identificação dos fatores ambientais em que este mais prolifera, de modo que se consiga fazer uma gestão apropriada das populações das espécies-alvo deste trabalho, que são um recurso de extrema importância económica para a área em estudo, de forma a garantir a sustentabilidade das mesmas.
Sardine (Sardina pilchardus) and horse mackerel (Trachurus trachurus) are two species that present an enormous importance at the level of marine trophic chains and with an elevate commercial value, presenting a peculiar importance in the Iberian Peninsula, where they are part of the portuguese traditional diet. The sardine and horse mackerel populations exhibit fluctuations on its stocks, however, the origin of these isn’t totally known. One of the known causes for the mortality in the early life phase (egg), is the parasitism by Ichthyodinium chabelardi, an endoparasite of pelagic fish eggs, where the sardine and horse mackerel are included, which ends up, in all known cases, leading to its host’s death. This work had two main objectives: (i) study the prevalence of infection by Ichthyodinium chabelardi in sardine and horse mackerel eggs; (ii) to analyse the special distribution of the infected eggs in the study area (south and west coast of atlantic Iberian waters), in consideration of some ambiental factors. Thus, it was proceeded the analysis of ichthyoplankton samples of 10 campaigns (in 7 of these were analyzed sardine eggs and in 5 mackerel eggs), and it was made the classification of the eggs by development stage and infection level. An additional objective considered the analysis of the possible mechanism of infection of the eggs by the parasite. For this purpose, it was explored the hypothesis of infection in the adult phase (before the oocytes emission) and developed molecular analysis protocols for the detection of the parasite in sardine gonads. The results showed that the percentage of eggs infected by the parasite (prevalence) in the analysed years varied between 0,80% and 4,32% in sardine eggs and between 0,82% and 10,97% in horse mackerel eggs and that the percentage of stations with parasitized eggs (PEOP) varied between 2,53% and 15,32% in the case of sardine eggs and between 2,00% and 12,59% in the case of horse mackerel eggs. It was possible to identify the depth as a possible ambiental factor responsible for these fluctuations, as well as the geographical location (west coast vs south coast) and the temperature (the last one only for sardine) trough effected GLM analyses, in which certain environmental factors were taken as independent variables and the number of parasitized eggs as the dependent variable. When the total mortality of sardine eggs was compared with the prevalence of infection in the same years, it was possible to verify that the years with the highest percentage of total mortality were also the years with the highest prevalence of infection by the parasite.The results relating to molecular analysis, that indicted the presence of Ichthyodinium chabelardi DNA fragments in the sardine gonads, seems to indicate that part of the life cycle of the parasite takes place in the adult stage of the host, and that the oocytes, when expelled by the females, may already be contaminated by the parasite, lacking, however, this information of confirmation by the sequencing of the DNA fragments thought to be from the parasite.Therefore, it becomes evident the importance of the better understanding of Ichthyodinium chabelardi life cycle and of deepen the identification of the environmental factors where it proliferates the most, in order to properly manage the populations of the target species of this work, which are an extremely important economical resource for the area under study, to ensure their sustainability.
Sardine (Sardina pilchardus) and horse mackerel (Trachurus trachurus) are two species that present an enormous importance at the level of marine trophic chains and with an elevate commercial value, presenting a peculiar importance in the Iberian Peninsula, where they are part of the portuguese traditional diet. The sardine and horse mackerel populations exhibit fluctuations on its stocks, however, the origin of these isn’t totally known. One of the known causes for the mortality in the early life phase (egg), is the parasitism by Ichthyodinium chabelardi, an endoparasite of pelagic fish eggs, where the sardine and horse mackerel are included, which ends up, in all known cases, leading to its host’s death. This work had two main objectives: (i) study the prevalence of infection by Ichthyodinium chabelardi in sardine and horse mackerel eggs; (ii) to analyse the special distribution of the infected eggs in the study area (south and west coast of atlantic Iberian waters), in consideration of some ambiental factors. Thus, it was proceeded the analysis of ichthyoplankton samples of 10 campaigns (in 7 of these were analyzed sardine eggs and in 5 mackerel eggs), and it was made the classification of the eggs by development stage and infection level. An additional objective considered the analysis of the possible mechanism of infection of the eggs by the parasite. For this purpose, it was explored the hypothesis of infection in the adult phase (before the oocytes emission) and developed molecular analysis protocols for the detection of the parasite in sardine gonads. The results showed that the percentage of eggs infected by the parasite (prevalence) in the analysed years varied between 0,80% and 4,32% in sardine eggs and between 0,82% and 10,97% in horse mackerel eggs and that the percentage of stations with parasitized eggs (PEOP) varied between 2,53% and 15,32% in the case of sardine eggs and between 2,00% and 12,59% in the case of horse mackerel eggs. It was possible to identify the depth as a possible ambiental factor responsible for these fluctuations, as well as the geographical location (west coast vs south coast) and the temperature (the last one only for sardine) trough effected GLM analyses, in which certain environmental factors were taken as independent variables and the number of parasitized eggs as the dependent variable. When the total mortality of sardine eggs was compared with the prevalence of infection in the same years, it was possible to verify that the years with the highest percentage of total mortality were also the years with the highest prevalence of infection by the parasite.The results relating to molecular analysis, that indicted the presence of Ichthyodinium chabelardi DNA fragments in the sardine gonads, seems to indicate that part of the life cycle of the parasite takes place in the adult stage of the host, and that the oocytes, when expelled by the females, may already be contaminated by the parasite, lacking, however, this information of confirmation by the sequencing of the DNA fragments thought to be from the parasite.Therefore, it becomes evident the importance of the better understanding of Ichthyodinium chabelardi life cycle and of deepen the identification of the environmental factors where it proliferates the most, in order to properly manage the populations of the target species of this work, which are an extremely important economical resource for the area under study, to ensure their sustainability.
Descrição
Relatório de estágio de mestrado, Ecologia e Gestão Ambiental, Universidade de Lisboa, Faculdade de Ciências, 2022
Palavras-chave
parasitismo Ichthyodinium chabelardi prevalência ovos de peixe Sardina pilchardus Trachurus trachurus Relatórios de estágio de mestrado - 2022