EFFECT OF DIETARY MOISTURE ON GROWTH AND INTESTINAL HISTOLOGY IN SERIOLA DORSALIS. A PRELIMINARY ASSESSMENT OF A NOVEL MOIST FEED  

Mark Portman1*, Daniel Benetti1, Rick Barrows2, Jorge Suarez1
1University of Miami: Rosenstiel School of Marine and Atmospheric Sciences
4600 Rickenbacker Causeway, Miami, Fl, 33149// mportman21@gmail.com
2 United States Department of Agriculture, Agricultural Research Service
Trout-Grains Project, Bozeman, MT USA

Commercial aquaculture feeds most commonly contain less than 10% moisture, while natural diets of carnivorous marine fish (i.e. forage fish, crustaceans) contains roughly 70% moisture and provides an important dietary source of fresh water. Following ingestion, marine teleosts hydrate dry formulated pellets via luminal secretions and ingested seawater. The pathways enabling absorption and excretion of salts, consequent of seawater drinking, are energetically costly to marine fish. Supplementation of feed with increased moisture content and decreased osmolarity may reduce the requirement for exogenous chyme hydration. We hypothesize that the use of feeds with a high moisture content may decrease this osmoregulatory cost/disturbance. This study examines the effect of dietary moisture content on growth and intestinal histology in California Yellowtail, Seriola dorsalis.

The industry standard for feed production requires cooking extrusion and drying to <10% moisture, which aids in spoilage prevention. Forgoing the drying process of this method may yield a moisture level of 25%, but water stability and nutrient retention of the feed are impaired. A modification to this extrusion method allows for the production of water stable particles with up to 55% moisture.

An 8-week feeding trial was conducted at Hubbs/Seaworld in San Diego, CA on juvenile S. dorsalis (25g).  A moist feed developed by the USDA-ARS, "Eco-Sardine" (ESM), was fed at two levels of moisture (5% and 50%).  A third group was fed a commercial control diet (CONT)(5% moisture). Dietary ration was calculated on a dry-weight basis.

The initial results illustrate that an increase in dietary moisture content had a negative effect on growth. Comparable growth among dry diets suggest that formulation or processing method do not explain the divergence in growth observed in the high-moisture treatment. The results from histological analysis, mycotoxin contamination test and proximate composition are pending and will be presented at the conference.