Parental investment in Arapaima gigas includes nest building and guarding, followed by a care provision when a cephalic fluid is released from the parents’ head to the offspring. This fluid has presumably important functions for the offspring but so far its composition has not been characterised. In this study the proteome and peptidome of the cephalic secretion was studied in parental and non-parental fish using capillary electrophoresis coupled to mass spectrometry (CE-MS) and GeLC-MS/MS analyses. Multiple comparisons revealed 28 peptides were significantly different between males and parental males (PC-males), 126 between females and parental females (PC-females), 51 between males and females and 9 between PC-males and PC-females. Identification revealed peptides were produced in the inner ear (pcdh15b), eyes (tetraspanin and ppp2r3a), central nervous system (otud4, ribeye a, tjp1b and syn1) among others. A total of 422 proteins were also identified and gene ontology analysis revealed 28 secreted extracellular proteins. From these, 2 hormones (prolactin and stanniocalcin) and 12 proteins associated to immunological processes (serotransferrin, α-1-antitrypsin homolog, apolipoprotein A-I, and others) were identified. This study provides novel biochemical data on the lateral line fluid which will enable future hypotheses-driven experiments to better understand the physiological roles of the lateral line in chemical communication.

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The Giant of Amazon basin, pirarucu, Arapaima gigas, is the largest scaled freshwater fish in the world. Pirarucu cultivation has recently started, driven by the decline in natural populations and high market value. Currently, there are no reliable methods for sexual differentiation in this species other than direct examination of gonads, which requires dissection of specimens. A non-lethal and less invasive method for sexual identification is highly desirable in order to properly group broodstock for mating and offspring production. We utilized laparoscopic examination in anesthetized pirarucu to differentiate between male and female individuals. This method allowed for the observation and differentiation of the reproductive organs within an individual. Our results suggest that laparoscopy is an efficient method for sex differentiation in pirarucu causing minimal stress to the fish. Determinação do sexo no peixe gigante da Bacia Amazônica, Arapaima gigas (Osteoglossiformes, Arapaimatidae), usando laparoscopia.O gigante da bacia amazônica, pirarucu, Arapaima gigas, é o maior peixe de escamas de água doce do mundo. O seu cultivo teve início recentemente motivado pelo declínio de suas populações naturais em virtude do alto valor de sua carne no mercado. Não existem métodos para a diferenciação sexual nesta espécie, o único método é o exame direto das gônadas, o qual requer a dissecação do espécime. Um método para a identificação sexual é altamente desejável, a fim de selecionar grupos de reprodutores para o acasalamento e, portanto, a produção de progênie. A fim de diferenciar reprodutores machos de fêmeas, foi utilizado o exame laparoscópico em animais previamente anestesiados. Este método permitiu a observação dos órgãos abdominais, incluindo gônadas, com grande precisão. Os resultados mostram que a laparoscopia é um método eficiente para a diferenciação do sexo em pirarucu e causam o mínimo de stress para os animais.

No abstract