Publication Date

2017-04-26

Availability

Open access

Embargo Period

2017-04-26

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Marine Affairs and Policy (Marine)

Date of Defense

2017-03-15

First Committee Member

Daniel D. Benetti

Second Committee Member

Frederic T. Barrows

Third Committee Member

Mark A. Drawbridge

Fourth Committee Member

Jorge A. Suarez

Fifth Committee Member

Jill L. Richardson

Abstract

Standard, commercial aquaculture feeds contain less than 10% moisture, while the natural diet of most carnivorous marine fish (i.e. forage fish, crustaceans) contains between 60-80% 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. 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 helps prevent spoilage. 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 Research Institute in San Diego, CA on juvenile S. dorsalis (27g). A moist feed developed by the USDA-ARS, was manufactured and fed at two levels of moisture (5% and 50%). A third group was fed a commercial control diet (5% moisture). Dietary ration was calculated as % BW on a dry-weight basis and maintained across treatment groups. The results form a histological analysis indicate no difference in intestinal morphology among treatments. Histological indications of intestinal distress were absent from all treatment groups. Increased dietary moisture content had a negative effect on growth. A comparable growth rate among dry diets suggests that formulation or processing method did not explain the divergence in growth observed in the high-moisture treatment. Proximate composition of the juvenile California yellowtail was statistically different only in lipid content. The moist feed treatment had a significantly lower whole-body lipid content as well as hepatosomatic index.

Keywords

Fish Nutrition; Aquaculture; Yellowtail; Dietary Moisture; Growth; Intestinal Histology

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