Nutrition of the southern sea garfish Hyporhamphus melanochir: gut passage rate and daily consumption of two food types and assimilation of seagrass components

Abstract

The southern sea garfish Hyporhamphus melanochir fed on the seagrass Heterozostera tasmanica for 13 h during daylight, ingesting an estimated 3 gut volumes of plant matter, equivalent to 500 kJ d-I kg-' dry wt. No cellulase was detected in garfish digestive tissues, and gut pH was near neutral, but the pharyngeal mill efficiently triturated the seagrass tissue. Seagrass frond was assimilated at an efficiency of 38 % (organic matter). 28 % (energy). 50 % (protein) and 76 % (lipids), these being equivalent to the total components available in seagrass cell contents. Nocturnally emergent crustaceans were preyed upon by garfish over a period of 6 h and were processed at half the rate of seagrass. The daily energy intake, and probably assimilation, from this source was 223 W kg-' dry wt. Although the crustaceans consumed were only a third the quantity of seagrass, it was reasoned to be an essential source of protein, and at least as important as seagrass in satisfying the energy requirements of H. melanochir.