Different pathways in the larval development of the crab Ucides cordatus (Decapoda, Ocypodidae) and their relation with high mortality rates by the end of massive larvicultures

Abstract

One of the most limiting factors affecting the larval rearing of Ucides cordatus in the laboratory is a period of high mortality, which usually occurs late in the course of the larviculture during the metamorphosis from the zoeal to the megalopal phase. The objective of the present research was to analyze the post-embryonic development of U. cordatus on an individual basis and, in particular, to search for patterns linking disturbances in the molting process to the high larval death rates observed in massive larvicultures. A total of 50 larvae were individually reared from hatching to metamorphosis into the megalopal phase under controlled conditions, fed a combination of microalgae and rotifers. The survivorship rate was 70% until zoea V. The 35 surviving zoea V larvae followed two different pathways. Eleven underwent metamorphosis directly to megalopa, eighteen molted to zoea VI and six died as zoea V. In the last molting event, only two zoea VI larvae reached the megalopal stage, while the remaining sixteen died. In further observation under microscope, 13 of the dead zoea VI showed characteristics of the pre-molt stage and pereiopods disproportionably large in relation to the carapace. The observed pattern resembles the Molt Death Syndrome (MDS) described for other decapod species, in which larvae die in the late pre-molt phase of the molting cycle. We suggest that U. cordatus larvae develop disturbances in the molting process similar to the MDS described for other species and that these disturbances are related to a more complex pathway involving the emergence of larval stage zoea VI. (Linnaeus, 1763) em laboratório é um período de alta mortalidade, o qual usualmente ocorre no ϐim do curso da larvicultura durante a metamorfose da fase de zoea para a de megalopa. O objetivo da presente pesquisa foi analisar o desenvolvimento pósembrionário de U. cordatus em uma base individual e, em particular, procurar por padrões ligando distúrbios no processo de muda com as altas taxas de mortalidade observadas nas larviculturas massivas. Um total de 50 larvas foram cultivadas individualmente da eclosão até a fase de megalopa em condições controladas, alimentadas com uma combinação de microalgas e rotíferos. A taxa de sobrevivência foi de 70% até zoea V. As 35 larvas zoea V sobreviventes seguiram dois diferentes caminhos. Onze realizaram a metamorfose diretamente para megalopa, dezoito Pesq. Vet. Bras. 32(4):284-288, abril 2012 285 The larval development of the crab Ucides cordatus and their relation with high mortality rates by the end of massive larvicultures mudaram para zoea VI e seis morreram como zoea V. No último evento de muda, apenas duas larvas zoea VI atingiram a fase de megalopa, enquanto as dezesseis restantes morreram. Em investigação posterior sob microscópio, 13 das zoea VI mortas mostravam características de estágio de prémuda e pereiópodes desproporcionalmente grandes em relação à carapaça. O padrão observado lembra a Sín-drome da Morte na Muda (MDS) descrita para outras espé-cies de decápodes, na qua...

Eyestalk ablation affects larval morphogenesis in the swimming crab Portunus trituberculatus during metamorphosis into megalopae

“…These final stage zoeae had morphological features similar to megalopae, such as large chelipeds and long pleopods with natatory setae. This mortality pheno menon is known as 'moult-death syndrome' (Mann et al 1999), and it has also been documented in other brachyuran crabs such as Scylla paramamosain, Scylla serrata, and Ucides cordatus (Mann et al 1999, Hamasaki et al 2002a,b, Takano et al 2004, Silva et al 2012. Furthermore, our previous study demonstrated that there were significant variations in the morphology of Portunus trituberculatus megalopae cultured in 12 hatcheries in Japan.…”

“…Interestingly, when larvae are supplied with high levels of n-3 HUFA under optimal rearing conditions during seed production, the chelae and pleopods become excessively enlarged, which results in mass mortality because of incomplete moulting into MG. The old exuviae can not be shed because of the size of the chelae and walking legs, a phenomenon that is termed 'moult-death syndrome' (Mann et al 1999, Hamasaki et al 2002a, Silva et al 2012). Thus, the cause of moult-death syndrome may relate to the regulation of morphogenesis by the eyestalk neurosecretory system as a normal response to the rearing condition.…”

“…Accordingly, there has been an increase in the number of rearing trials to improve larval rearing techniques. As a result, there has been a concomitant increase in the number of reports documenting the existence of variations in larval morphology and a relationship with larval mass mortality during seed production (Hamasaki et al 2002a,b, 2011, Silva et al 2012. Arai et al (2004) reported that, during seed production of the swimming crab Portunus trituberculatus, morphologically advanced fourth stage (last stage) zoeae failed to shed their exuviae completely during their metamorphosis into megalopae and eventually died.…”

Importí­¢ncia do rotí­­fero como alimento no desenvolvimento larval do caranguejo-uçá

“…Entretanto, a degradação das florestas de manguezal, a pesca predatória e a doença do caranguejo letárgico têm reduzido os estoques e alterado a estrutura populacional (CASTILHO-WESTPHAL et al, 2008;VICENTE et al, 2012;GUERRA et al, 2013). Este fato, além de levar o governo brasileiro a promover a reclassificação do caranguejo U. cordatus como espécie sobre-explotada, demonstrou a necessidade do desenvolvimento de políticas e técnicas de manejo populacional (JANKOWSKY et al, 2006;GOES et al, 2010) e de ações para recuperação dos estoques naturais com pesquisas em produção de larvas e formas jovens em laboratório (ABRUNHOSA et al, 2002;SILVA et al, 2012).…”

“…Devido a esta importância, diferentes organismos têm sido utilizados no cultivo larval de U. cordatus por vários autores (RODRIGUES e HEBLING, 1989;ABRUNHOSA et al, 2002;DIELE e SIMITH, 2006;SOUZA et al, 2006;VENTURA et al, 2008;SILVA et al, 2012;COTTENS et al;2014), os quais reportaram a importância do fornecimento de alimento desde o primeiro estágio de zoea, para o qual microalgas ou náuplios de Artemia sp. podem não ser adequados, e que os melhores resultados foram obtidos utilizando diferentes combinações destes dois itens alimentares em conjunto com rotíferos (Brachionus sp.)…”