Parasitic copepods are common on marine fish, and there is a vast literature describing their taxonomy and the records on several hosts (^{BOXSHALL; HALSEY, 2004}). In the Neotropics, copepods are the second largest parasite group in marine fishes and the third largest group in the freshwater hosts (^{LUQUE; POULIN, 2007}). However, there are few records of parasitic copepods on clupeid fishes in this region, essentially due to lack of parasitological studies of these hosts (^{LUQUE; TAVARES, 2007}).

Sardinella brasiliensis (Steindachner, 1879) is a small pelagic fish, belonging to family Clupeidae, which form large schools, and according to Whitehead (1985) is distributed from Gulf of Mexico, Caribbean, West Indies southward to Brazil and northern Uruguay, but according to ^{Figueiredo and Menezes (1978)} the distribution of S. brasiliensis is restricted to southwest Atlantic, more specifically from Rio de Janeiro to south Brazil. The Brazilian sardinella is the commercially most important fish on the southeastern Brazilian coast and is used as fresh food, canned, or processed as fishmeal for animal feed, and supports the most important fishery, with total annual catches around 150.000 t (^{ROSSI-WONGTSCHOWSKI et al., 2003}; ^{TEODORO et al., 2007}).

Lernaeopodidae is a large and diverse family of highly specialized parasitic copepods, currently comprising 48 genera including Clavellisa Wilson, 1915, which consists of 12 nominal species (^{GURNEY, 1947}; ^{BOXSHALL; HALSEY, 2004}). Members of Clavellisa genus are host specific, and many species have been found associated with clupeiform fishes, particularly from Indian waters (^{RUBEC; HOGANS, 1987}; ^{EL-RASHIDY; BOXSHALL, 2010}).

One hundred specimens of Sardinella brasiliensis, collected from coastal zone of the State of Rio de Janeiro, Brazil (21-23°S, 41-45°W) were necropsied between march 2010 and august 2011, to study their biodiversity of metazoan parasites. Four specimens were parasitized by Clavellisa ilishae (Figure 1), indicating a prevalence of 4%. After collection, the copepods were fixed and preserved in ethanol (70% GL) and were clarified with lactic acid for identification. The taxonomic determination of the parasites was in accordance with the diagnosis proposed by ^{El-Rashidy and Boxshall (2010)}. Were collected a total of eleven specimens of C. ilishae, with a mean intensity of 2.75, all attached to the gills, and all copepods were sexually mature females. Specimens of C. ilishae (three females) were deposited in the Crustacea Collection of the National Museum, Rio de Janeiro (MNRJ No 23421).

Figure 1.  Clavellisa ilishae ^{Pillai, 1962}, female. a) Habitus; b) habitus (DIC electron micrograph); c) anal laminae; d) maxillae attached to bulla. 

The body of a lernaeopodid female has the maxillae fused to an anchoring structure known as a bulla, which is attached to the host (^{PIASECKI et al., 2004}). We identified C. ilishae from the shape of the trunk, broader than long and laterally rounded, the elongate cephalothorax, details of oral appendages and its short maxillary arms, and by the presence of small caudal rami, flanking the anal laminae, on the posterior margin of the trunk, reported, until the present moment, only on this species. The dimensions of the present specimens are comparable with those given by ^{Pillai (1962)}, ^{Kensley and Grindley (1973)} and by ^{El-Rashidy and Boxshall (2010)} (Table 1).

Clavellisa ilishae was originally described by ^{Pillai (1962)} and since its description this species has only been recorded parasitizing clupeiform hosts (Ilisha filigera, I. melastoma, Tenualosa ilisha, Sardinops sagax and Sardinella aurita) (^{KABATA, 1979}; ^{PILLAI, 1985}; ^{KENSLEY; GRINDLEY, 1973}; ^{EL-RASHIDY; BOXSHALL, 2010}). The presence of this copepod in S. brasiliensis corroborates with the theory of host specificity on the genus by clupeiform fishes proposed by ^{El-Rashidy and Boxshall (2010)}, which recorded C. ilishae parasitizing the Round sardinella Sardinella aurita in Egypt. Probably the dissemination of C. ilishae in the Neotropics occurred through the S. aurita, that is widely distributed in this region, inhabiting the continental shelves of the western Atlantic from Massachusetts (USA) throughout the Gulf of Mexico and Caribbean Sea to Rio de Janeiro (Brazil) and the eastern Atlantic at the African coasts, South Africa, and also on Mediterranean and Black Sea (^{FISCHER, 1978}; WHITEHEAD, 1985).

There are no records of parasitic copepods on S. brasiliensis, indeed there are few records of parasitic copepods in clupeid fishes at the Brazilian waters. ^{Montú (1980)} described the species Gauchergasilus (= Ergasilus) euripedesi parasitizing Brevoortia pectinata. ^{Amado and Rocha (1996)} described the species Acusicola brasiliensis parasitizing the gill filaments of Lile piquitinga and Opisthonema oglinum.

Lernaeopodids may affect their hosts through pathological effects, sometimes causing slight inflammation where the bulla is inserted into the host, but most damage is caused by the rasping action of the mandibles (^{FRYER, 1982}). The habit to form schools can favor the transmission of some parasites with direct life cycle, such as copepods and monogeneans. Thereby, a massive infestation could seriously damage the host and lead to large economic losses in commercially important fishes as Brazilian sardinella.