Exposure of Nile Tilapia (Oreochromis niloticus) Fingerlings to a Saxitoxin-Producing Strain of Raphidiopsis (Cylindrospermopsis) raciborskii (Cyanobacterium) Reduces Growth Performance and Increases Mortality Rate.

Blooms of toxin-producing cyanobacteria have been more frequent and lasting because of the eutrophication of freshwater ecosystems, including those used for aquaculture. The aim of the present study was to investigate the effects of chronic exposure to a saxitoxin-producing strain of Raphidiopsis (Cylindrospermopsis) raciborskii on the performance of Nile tilapia (Oreochromis niloticus) fingerlings over a 60-d period. The fingerlings were cultivated under the following conditions: 1) water without cyanobacterium (WATER), 2) R. raciborskii in ASM-1 culture medium (CYANO), and 3) ASM-1 culture medium without cyanobacterium (ASM). Exposure to the CYANO treatment led to a significant increase in the mortality rate (p < 0.05) and a significant reduction in growth (p < 0.05) compared to fingerlings submitted to the ASM and WATER treatments, in which similar survival and growth were found (p > 0.05). Saxitoxin toxicity was dependent on the weight of the fingerling (p < 0.05), with maximum mortality caused by the ingestion of 13.66 µg saxitoxin equivalent L-1 g-1 . The present results clearly show the harm caused by saxitoxins to the production of Nile tilapia fingerlings in the early growth phase. These findings underscore the importance of maintaining adequate water quality in aquaculture activities to minimize the risk of saxitoxin-producing cyanobacterial blooms and avoid economic losses among producers. Environ Toxicol Chem 2020;39:1409-1420. © 2020 SETAC.

Nutritional and performance viability of cactus Opuntia-based diets added to concentrate levels for Girolando lactating dairy cows.

OBJECTIVE: The aim of this research was to evaluate the effect of different concentrate levels in diets based on cactus Opuntia Stricta (Haw.) Haw cladodes over the performance of lactating Girolando cows. METHODS: The experiment involved 10 Girolando multiparous dairy cows (512.6 kg of body weight and producing 13.2kg milk/day), allocated into two 5 x 5 Latin squares. The experimental treatments consisted of control diet composed by cactus Nopalea cochenillifera. Salm-Dyck. cladodes (Nopalea), forage sorghum silage and concentrate (20% at DM basis), and four concentrate levels diets (20, 24, 28 and 32%) plus cactus Opuntia stricta (Haw.) Haw. cladodes (Opuntia) and forage sorghum silage. RESULTS: Regarding cows fed control diet, the nutrients intake were greater than for cows fed with cactus Opuntia and concentrate. Regarding concentrate levels, intakes of dry matter (DM), organic matter (OM), crude protein (CP), non-fiber carbohydrates (NFC) and total digestible nutrients (TDN) of cows increased linearly. The OM, CP and NDF digestibilities were similar in between to control diet and cactus Opuntia-based diets. The digestibility of NFC increased linearly when the concentrate was inserted. The N balance was the same for control diet and cactus Opuntia-based diets, irrespective the concentrate levels. CONCLUSION: For cows producing 14 kg/day with 3.5% of fat, it is recommended 32% of concentrate inclusion in cactus Opuntia-based diets, and the increase in concentrate level promotes a linear increase in milk yield.