The cleaner fish Elacatinus figaro can control the monogenean Neobenedenia melleni, an ectoparasite of Lebranche mullet Mugil liza and does not decrease the hematological response.

This study aimed to evaluate the hematological parameters of mullet (Mugil liza) naturally parasitized by Neobenedenia melleni after cohabitation with the barber neon goby (Elacatinus figaro) as a biological control (cleaner fish) of ectoparasites. A total of 108 mullets were distributed in 500 L tanks, with six mullets per tank, in triplicate, divided into six groups: naïve (without neon and non-parasitized), mullets parasitized with N. melleni in cohabitation with one, two, three, and six neons, and the control (without neon and parasitized). Continuous aeration in a static system and a 12-h photoperiod for a period of 25 d was used. For hematological analyses, blood samples were collected from six fish per experimental unit. Blood was used to determine the hematocrit, hemoglobin concentration, total erythrocyte count, mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), total thrombocyte and white blood cell counts, as well as the differential leukocyte count. Erythrocyte and lymphocyte counts were higher in the only parasitized group without cleaner fish (control) compared to the groups that had 1, 2, 3 and 6 neon and parasitized with N. melleni and the naïve group. In addition, the mullet circulating monocytes increased in the control groups and in the animals that were cohabiting with 6 neons compared to the naïve. The MCHC was reduced in the control group compared to naïve. Fish from treatments with 1, 2, and 3 neons showed similar hemogram values among themselves and to the naïve group, indicating lower stress in aquaculture systems with E. figaro acting as a biological control.