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The objective of this study was to characterize and compare the hematological variables (erythrogram, thrombogram, leukogram and plasma metabolites) of three cichlid species: Cichla monoculus, Cichla temensis and Cichla vazzoleri. A total of 45 specimens were captured in Balbina lake, Presidente Figueiredo, Amazonas, Brazil, with the aid of a rod and reel or hand line, with natural or artificial bait: 15 C. monoculus, 15 C. temensis and 15 C. vazzoleri. Their blood was removed by means of caudal puncture of the dorsal aorta, and hematological data were determined in accordance with methodology previously described in the literature. The erythrogram showed similarities between the species, while the thrombogram showed differences between C. vazzoleri and the other species studied (C. monoculus and C. temensis). The total leukocyte counts for C. temensis and C. vazzoleri were higher than those of C. monoculus. The predominant leukocyte in C. temensis and C. vazzoleri was lymphocytes, whereas it was monocytes in C. monoculus. The plasma metabolites showed differences between the three cichlid species, regarding their glucose, cholesterol, urea and potassium levels. It is concluded that these three species present hematological differentiation, thus indicating that they have differentiated blood-cell immune responses and plasma metabolite physiology.

We evaluated the effect of the light-dark (LD) cycle on energy expenditure indicators for two species of Amazonian fish of commercial interest, oscar (Astronotus ocellatus) and matrinxã (Brycon amazonicus). Fish were exposed to a 12:12 h LD cycle, with lights on at 'zeitgeber time' (ZT) = 0 h. Six animals were used for blood collection every 4 h for 24 h (six time points, three in the light period and three in the dark period).Most haematological parameters exhibited daily rhythms with the acrophase at the end of the dark phase or the beginning of the light period for both species, which may be related to the greater energy demand of these species during the day. For A. ocellatus, triglycerides and total protein showed acrophases at ZT = 13:32 ± 2:45 h and ZT = 23:42 ± 1:55 h, respectively, while the other plasma parameters showed no significant daily differences. In B. amazonicus, significant rhythms were observed for glucose levels (acrophase at ZT = 04:16 ± 2:47 h), triglycerides (ZT = 6:51 ± 4:06 h) and total cholesterol (ZT = 23:22 ± 3:45 h). However, total protein and cortisol levels did not show rhythmicity in this species. Our results highlight the importance of the evaluation of biological rhythms for plasma physiological parameters related to energy expenditure in species with commercial interest and susceptible to stressful situations in farming conditions.

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