Authors: Moti Harel, William Koven, Eric. D. Lund, Paul Behrens and Allen R. Place

Center of Marine Biotechnology, University of Maryland, Baltimore , Maryland 21202, USA. harel@umbi.umd.edu

(Abstract presented at the 1998 World Aquaculture Society meeting in Las Vegas, Nevada)

Abstract

Eggs of marine fishes contain markedly higher levels of DHA (docosahexaenoic acid), ranging from 10-40% of total fatty acids, and generally a ratio of DHA:EPA (eicosapentaenoic acid) greater than 2:1. This suggests that the early development of the larvae requires high levels of DHA for optimal growth and survival. Standard enrichment procedures for rotifers and Artemia nauplii, however, do not provide the required levels of DHA and DHA:EPA ratios. We report that this goal has now been achieved by using a spray-dried phospholipid extract of DHA-rich Crypthecodinium sp. algal biomass (Martek Biosciences Corporation, Columbia, Maryland, USA) of which the total fatty acids are 49% DHA and less than 0.5% EPA.

Enrichment of stage II Artemia nauplii was carried out at 28-30°C, in aerated 20 ppt artifial sea water (200,000 nauplii/liter). Two equal portions of 0.3g DHA-rich phospholipids/liter were given at time 0 and after 8 hours. A significant increase (P <0.05) in nauplii lipid content from an initial level of 16.3% to 23.7% dry weight (D.W.) was obtained after 16 hours. DHA increased from undetectable levels to 41mg/g D.W. (17.2% of total fatty acids), while EPA content increased only slightly from 5% to 6.2% of total fatty acids. Similar enrichment patterns were also observed with the rotifer, Brachionus plicatilis. Using this process of DHA-rich phospholipids enrichment, feeding experiments with Sea Bream (Sparus aurata) larvae demonstrated better growth and swimbladder inflation rates when fed on high DHA-enriched food organisms relative to larvae fed on food organisms enriched with other commercial preparations.

In an effort to determine the most effective molecular carrier of DHA for larval food organisms enrichment, we tested the hypothesis of whether DHA-ethyl esters or DHA-containing phospholipids could improve Artemia enrichment. Different enrichment treatments having varying proportions of phospholipids and ethyl esters at a constant level of DHA were fed to the nauplii. A significant (P <0.05) higher absorption of 31% DHA by Artemia was obtained during the first 8 hours at 10% dietary phospholipids level compared to 5%, while no further improvement in absorption was obtained at higher phospholipid percentages or with the addition of any level of free fatty acids. The triacylglycerol : phospholipid ratio in the nauplii was independent of this ratio in the enrichment diets (p <0.05), further results show that Artemia survival was not affected even at dietary phospholipid levels of 40%. These results imply that the phospholipid extracts of DHA-rich Crypthecodinium sp. algal biomass provide an effective DAH enrichment of food organisms for the enhancement of growth and survival in marine fish larvae culture.

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Single Cell Heterotrophs Carriers of Advanced Enrichment Elements for Marine Aquaculture

Authors: Moti Harel*, William Koven, Allen R. Place

The Center of Marine Biotechnology, University of Maryland, 701 East Pratt Street, Baltimore, MD. 21202 USA

Source: 2001 American Aquaculture Society Conference, San Diego, CA.

See Enrichment Comparison Chart.

The heterotrophic, large-scale production of algal biomass represents a potential high quality substitute for fish ingredients in aquaculture feeds. These sources can be particularly rich in docosahexaenoic acid (DHA), arachidonic acid (ArA) and carotenoids, which are required in larval growth and survival as well as contributing to egg and sperm quality when included in broodstock diets. Algal species such as Crypthecodinium cohnii can produce oils with up to 50% docosahexaenoic acid (DHA), while the spray-dried biomass from Nitzschia sp., and Navicula sp. can offer a rich source of eicosapentaenoic acid (EPA). Moreover, oil extracts containing up to 54% ArA from the heterotrophic fungi Mortierella sp., have been combined with these omega-3 rich algal products to produce uniquely balanced enrichment formulations. In a series of studies, we tested the use of heterotrophically grown microalgae and its extracted oil as sources of nutrients and essential fatty acids for rotifers and Artemia which are then passed on to the fish larvae. We also studied these new formulations in broodstock feeds. The improved enrichment resulted in enhanced growth and survival under stressful conditions of several marine larvae species, including seabream, European sea bass, Atlantic halibut, and striped bass. The inclusion of heterotrophically grown algae meal and oil extracts in striped bass broodstock diets resulted in spawning levels and hatching rates exceeding those obtained with standard commercial diets.

In cases where disease outbreak is anticipated, stimulating the defense mechanisms in larvae may reduce losses. We have discovered that certain new dietary formulations containing ArA can dramatically improve the response of larvae to pathogen challenge and significantly increase post stress survival. Because marine algae are major part of the fish food chain in the nature, they can also be used as carriers for oral delivery of anti-vibrio elements and immunity enhancers during the early life stages of the animal. Our screening for antibacterial activities has indicated that several microalgae species exhibit strong antibacterial or bacteriostatic capabilities. These algal species are now being tested for there effectiveness as a high value enrichment feed that delivers both nutritional value and disease control elements in the same package.

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