Economic feasibility of probiotic use in the diet of Nile tilapia, Oreochromis niloticus, during the reproductive period

This work examines the economic advantages of probiotic use in the diet of Nile tilapia broodstock during the reproductive period. For this purpose, Bacillus subtilis was applied as a feed additive. The experimental design was completely randomized with three treatment groups: the T0 control (without probiotic), the T1 continuous probiotic intake, and the T2 alternate probiotic intake at a dose of 0.50 g kg-1 of feed (1010 CFU g-1) with four replicates. For the reproduction assay, 118 females and 48 males of Nile tilapia (proportion 4 males:9 females. hapa-1) (weight 527.65 g ± 185.98 g and length 30.16 cm ± 3.57 cm) were distributed into 12 hapas (3.5 × 2.0 × 1.5 m). Reproductive variables (spawning female percentage, egg production, and fry production) were used to calculate the economic feasibility indexes (total cost of nutrition [TcN], gross revenue [GR], and total operational profit [ToP]). The results show increasing values for spawning female number, collected eggs, and surviving fry in the probiotic groups. We recommend continuous intake of probiotic (feed with addition of probiotic) at a dose of 0.5 g kg-1 of feed (1010 CFU g-1) during the breeding season of Nile tilapia, due to the suitable reproductive indexes and profitability.

Impact of waterborne and trophic mercury exposures on cardiac function of two ecologically distinct Neotropical freshwater fish Brycon amazonicus and Hoplias malabaricus

Metal pollutants have been considered one of the main factors underlying the depletion of biodiversity in natural populations unbalancing aquatic environments. The aim of this study was to evaluate the effects of exposure to inorganic Hg on myocardial contractility and the electrocardiogram (ECG) of two ecologically distinct Neotropical fish species, namely: matrinxã (Brycon amazonicus) and trahira (Hoplias malabaricus). Matrinxãs were exposed to a sublethal concentration of 0.1mgL^-1 of Hg in water for 96h. Trahiras were exposed to dietary Hg doses (0.45mg of Hg, each 4days, for 30days) using juvenile B. amazonicus as the prey vehicle. Hg exposures decreased myocardial isometric twitch force development, harmed contraction/relaxation dynamics and cardiac pumping capacity (CPC), and reduced the relative contribution of the calcium stored in the sarcoplasmic reticulum (SR) to excitation contraction (EC) coupling in both fish species. Analysis of the ECG revealed that Hg impaired electrical conduction across the heart, inducing first degree atrioventricular block and lengthening the plateau phase of action potential duration. In trahira trophic doses of Hg induced a marked bradycardia, increasing the duration of the ventricular action potential and delaying atrial and ventricular depolarization. These findings indicate that both acute and long-term Hg exposure, by different routes is cardiotoxic to matrinxã and trahira. Hg potently impaired intracellular calcium kinetics in the cardiomyocytes, myocardium contractility, and electrical conduction across the heart, all of which can be implicated in decreased cardiac output and putative heart failure.