Hugh S. Hammer

Validation of Dual‐energy X‐ray Absorptiometry to Predict Body Composition of Channel Catfish, Ictalurus punctatus

Dual-energy X-ray absorptiometry (DXA) provides a noninvasive way to determine lean tissue mass (LTM), fat mass (FM), bone mineral content (BMC), and bone mineral density (BMD) in humans and small mammals. Live channel catfish (n=74, 78g - 1200 g) were anesthetized and scanned in both a lateral position and a dorsa-ventral position. Six individual fish (300g - 600g) were scanned five times each to determine precision by the coefficient of variation. Precision was good for LTM (0.75-1.06%) and for BMC and BMD (2-2.6%). Precision for FM was not good (27-34%), which was due to the very low FM (0-1g) recorded by the DXA. However, using the predicted values, FM precision improved to 5-5.5%. DXA values for LTM, FM, and BMC were significantly different from chemical analysis (P< 0.001). DXA overestimated LTM and underestimated FM and BMC. However, all three compartments were strongly correlated with carcass values (P <0.0001). Using the prediction equations and the jackknife procedure, predicted values of LTM, FM, and BMC were not significantly different from the carcass values (P >0.05). DXA may also be a valuable tool for evaluating body condition longitudinally in commercial or in threatened or endangered fish species, where non-invasive procedures would be invaluable.

Dietary Copper Affects Survival, Growth, and Reproduction in the Sea Urchin Lytechinus variegatus

ABSTRACT Copper is an essential micronutrient in the diets of animals. It is a component of many enzymes involved in energy production, participates in immune function, and protects cells from free radicals. However, excessive levels in the diet can be toxic. Small (∼13 g wet weight) Lytechinus variegatus were fed formulated feeds with 12, 36, or 114 mg Cu/kg for 12 wk (levels based on established dietary levels for other marine invertebrates, supplemented as CuSO4·5H2O). Under these experimental conditions, wet weights of individuals fed a 36-mg Cu/kg diet were slightly higher (43.2 ± 1.2 g (SEM); P = 0.069) than those fed a 12mg Cu/kg and 114-mg Cu/kg diet (39.9 ± 1.2 and 40.3 ± 1.7 g wet weight, respectively). Ovary and gut wet weights were significantly lower (P < 0.003) in the 114-mg Cu/kg diet than the 12-mg Cu/kg and 36-mg Cu/kg diets (7.24 ± 0.75 g, 8.11 ± 0.55 g, and 4.99 ± 0.32 g ovary wet weight and 0.97 ± 0.04 g, 1.07 ± 0.06 g, and 0.83 ± 0.04 g gut wet weight for the 12-, 36-, and 114-mg Cu/kg diets, respectively). Mature gamete formation in ovary and testis was inversely correlated with dietary copper level. Acini from the ovaries and testis of urchins in the 36-mg Cu/kg and 114-mg Cu/kg diet treatments had a greater area occupied by nutrient phagocytes than urchins on the 12-mg Cu/kg diet. In diets containing low dietary copper (12 mg Cu/kg), survivorship decreased from 100% to 87%. These data suggest that dietary copper is essential for normal physiological function but can be detrimental for certain physiological processes at high levels. This information will help in the development of formulated feeds for sea urchin aquaculture.