P. O. Maciel

Myxobolus sp. (Myxozoa) in the circulating blood of Colossoma macropomum (Osteichthyes, Characidae)

Myxosporea parasitize many organs in fresh and saltwater fish. Species of the genus Myxobolus parasitizing the gills and other organs of the tambaqui Colossoma macropomum have been described. In the present study, blood smears were made from juvenile tambaqui and were stained with May Grunwald-Giemsa-Wright in order to identify myxozoan parasites. Out of a total of 36 fish examined, one specimen (2.7%) that was reared in a cage presented spores that were identified as M. colossomatis, whereas fish kept in 250 L tanks showed prevalence of 5.5%. This is the first report of M. colossomatis in the blood of farmed tambaqui in the Amazon region. These results indicate that myxozoan parasites should also be investigated in fish blood smears. Some myxosporean species may cause diseases in fish, and these species need to be identified so that adequate preventive sanitary control can be instituted.

Trichodinidae in commercial fish in South America.

Ciliates of the family Trichodinidae are protozoan parasites of importance for fish farming in South America, given that at high infestation levels, they cause significant mortality among farmed fish. Although data on economic losses due to parasitosis are not available for South America, mortality outbreaks correlated to trichodinids are very common in the tilapia production chain, especially in Brazil, the largest aquaculture chain in the country. In Brazil in the past, trichodinids were considered only as Trichodina sp. Today, they have been better studied and identified taxonomically in wild and farmed fish. However, in other countries in South America, trichodinids continue to be described only as Trichodina sp. This review presents the history of occurrences of trichodinids in fish of interest in South America, highlighting 15 new species that have been described in three genera in Brazil, along with information on parasite-host-environment relationships, diagnostic methods and treatments. The occurrence of parasitic ciliates must be correlated with farming conditions such as stress factors, water quality, seasonality, age and host immunity to elucidate the critical points of each production system. Furthermore, for tropical fish, studies on treatment against trichodinid species are needed to provide support for approval of antiparasitic medications for use in fish farming. However, it is recommended that the production sector use intensive production systems that are more sustainable, with biosafety protocols, to increase production and productivity.

Eggs hatching and oncomiracidia lifespan of Dawestrema cycloancistrium , a monogenean parasitic on Arapaima gigas

Within the production chain of the Arapaima gigas (pirarucu), sanitary issues are still faced at the fingerling phase regarding infestations by the monogenean Dawestrema cycloancistrium. The present study had the objectives of describing the morphology and development phases of this parasites eggs and oncomiracidia and determining the hatching time and lifespan of the oncomiracidia at different temperatures. D. cycloancistrium eggs were oval and elongated and had a single long appendage at one pole. The egg development was divided into four phases: embryonated egg, developing egg, larva appearance and ecloded egg. They were found in four forms: isolated in gill filaments; grouped in clusters that were anchored in a gill filament; grouped in clusters and entangled in part of a dead adult monogenean; and grouped in clusters in the environment, fixed to a substrate. Eclosion occurred after 72-96h, with faster development at 29°C and 32°C than at 24°C. The morphology of the oncomiracidia were rounded and elongated. They had two pairs of pigmented eye-spots as well as two ciliated areas located on each lateral part of the body and another on the anterior part of the body. The lifespan of the D. cycloancistrium oncomiracidia were 50 and 58h at 24°C and 27°C, respectively. Larvae were found in the mucus, indicating that the oncomiracidia penetrated the host integument. Understanding reproductive aspects of the D. cycloancistrium monogenean is important for developing specific prophylactic management strategies in aquaculture and providing valuable data for further studies.