Dynamics of Energy Storage in a Freshwater Predator (Nephelopsis obscura) following Winter Stresses

Abstract

Two groups of Nephelopsis obscura were maintained under identical conditions (20 °C, 100% dissolved oxygen, 12 h light: 12 h dark regime, ad libitum food) from post-hatchling size (10–11 mg) to sexual maturity (500–700 mg). One group (winter N. obscura) had overwintered in the field and degrown to 10–11 mg, while the other group (summer N. obscura) had hatched in the laboratory. The winter N. obscura at post-hatchling size had significantly lower accumulations of total lipid (3.9%), total protein (50.7%), free amino acids (1.6%), and glycogen (3.4%) than summer leeches, indicating that winter stresses (low water temperatures, low dissolved oxygen, restricted prey availability) had reduced energy stores and caused degrowth. The cryoprotective glycerol concentration, however, was significantly higher (1.9%) in winter leeches. At or just prior to sexual maturity, both winter and summer leeches showed decreases in total protein, glycogen, and total lipid which were attributed to the increased energetic demands of gametogenesis and maturation. The effects of, and compensation for, winter stresses were evident throughout the development of the winter leeches which exhibited enhanced energy allocation to storage compared with summer leeches.