Effects of biodensity on the growth, stress physiology, and welfare of Arctic charr (Salvelinus alpinus) in freshwater.

Biodensity is a major factor affecting the production and welfare of farmed fishes. Arctic charr (Salvelinus alpinus) (average mass 176.9 ±â€¯3.9 g) were held at biodensities of 30, 60, 90, 120, and 150 kg/m3 (4 replicates per treatment) during a 91 day study which examined key growth, stress physiology, and welfare parameters. During experimentation fish were fed to near satiety, and a random subsample of 20 fish (5 per replicate tank) were collected from each treatment every 21 days. Biodensity was found to have no significant effect on mortality rates or physical fin damage. Growth rates were lower in charr reared at the highest biodensities (120, and 150 kg/m3), while feed efficiency was negatively affected at both the highest (120, and 150 kg/m3) and lowest (30 kg/m3) biodensities. Plasma cortisol indicated that Arctic charr are more stressed at lower biodensities, but was not correlated with growth or feed efficiency measures. The results support an optimal biodensity range for charr culture between 60 and 90 kg/m3 to optimize production and welfare.

Widespread Natural Occurrence of Hydroxyurea in Animals.

Here we report the widespread natural occurrence of a known antibiotic and antineoplastic compound, hydroxyurea in animals from many taxonomic groups. Hydroxyurea occurs in all the organisms we have examined including invertebrates (molluscs and crustaceans), fishes from several major groups, amphibians and mammals. The species with highest concentrations was an elasmobranch (sharks, skates and rays), the little skate Leucoraja erinacea with levels up to 250 µM, high enough to have antiviral, antimicrobial and antineoplastic effects based on in vitro studies. Embryos of L. erinacea showed increasing levels of hydroxyurea with development, indicating the capacity for hydroxyurea synthesis. Certain tissues of other organisms (e.g. skin of the frog (64 µM), intestine of lobster (138 µM) gills of the surf clam (100 µM)) had levels high enough to have antiviral effects based on in vitro studies. Hydroxyurea is widely used clinically in the treatment of certain human cancers, sickle cell anemia, psoriasis, myeloproliferative diseases, and has been investigated as a potential treatment of HIV infection and its presence at high levels in tissues of elasmobranchs and other organisms suggests a novel mechanism for fighting disease that may explain the disease resistance of some groups. In light of the known production of nitric oxide from exogenously applied hydroxyurea, endogenous hydoxyurea may play a hitherto unknown role in nitric oxide dynamics.