Dissertation/Thesis Abstract

Effect of a docosahexaenoic acid devoid diet on medaka Oryzias latipes
by Ruiz Ramos, Alejandro, Ph.D., University of California, Davis, 2013, 175; 3614268
Abstract (Summary)

The effect of a Purified Casein-based diet devoid of highly unsaturated fatty acids (HUFA) (docosahexaenoic acid- diet, DHA- diet) was investigated on medaka Oryzias latipes by replacing cod liver oil with mid-oleic sunflower oil. In Chapter 1, the growth and reproduction performance of adult medaka was investigated. Fatty acid composition of gonads from females fed either the DHA- or DHA+ diet for 32 weeks and from first generation of larvae fed the DHA- diet through adulthood was evaluated as well. Significant differences in body weight were observed only on males fed the DHA+ diet when weighed at day 66 of dietary treatment (20.6% weight gain). Fecundity and fertility of females fed either the DHA- or DHA+ diet decreased over time. However, declines were greater on the females fed the DHA- diet. Gonadal DHA and eicosapentaenoic acid (C20:5n-3, EPA) content, expressed as percent of total fatty acids (% TFA) reflected that of the diet given. Gonadal DHA% TFA of females given the DHA- diet was 82% and 54% lower (generation zero and first generation, respectively) than generation zero fed the DHA+ diet. In Chapter 2, the effect of the DHA- diet on embryo wet weight and fatty acid composition through 91 days of embryo collection was investigated. Relationships of selected fatty acids of embryos at four different time points from breeders given either a DHA- or DHA+ diet were calculated as well. Enzymes index of activity for desaturases and elongases were obtained from fatty acids product-to-precursor ratios in embryos. Embryo DHA and EPA content resembled that of the diet given to the breeders. For EPA in embryos from a DHA- diet, the best fit is a transformed fit natural log, whereas for embryos from DHA+ diet it is a quadratic fit. For ARA in embryos from DHA- diet the three curves fit well. The high delta6- and delta5-desaturase indices coincide with the higher gamma linolenic acid (18:3n-6, GLA) and ARA% TFA in embryos from breeders given the DHA- diet compared to embryos from breeders given the DHA+ diet. By contrast, the higher elongase-5 activity and the lower desaturase activity in embryos from breeders given the DHA+ diet reflect the accumulation of the products EPA, docosapentaenoic acid (C22:5n-3, DPA) and subsequently DHA. Embryos from medaka fed the DHA- diet weighed more (1.036 ± 0.004 mg/embryo, n = 779) than embryos from medaka given the DHA+ diet (0.948 ± 0.008 mg/embryo, n = 564). ARA is required for oocyte maturation and hydration. The DHA- diet lacked HUFA, whereas the DHA+ diet contained DHA, EPA and ARA. DHA- diet contained significantly more linoleic acid (C18:2n-6, LA) (44.15% TFA) (precursor of ARA) than ALA (C18:3n-3, alpha linolenic acid) (34.0% TFA) (precursor of EPA and DHA). It is suggested that in medaka there is a HUFA synthesis system similar to in zebrafish ovary (Ishak et al. 2008) and that in the absence of dietary DHA, embryo DHA is depleted and therefore LA is predominantly converted enzymatically to ARA, subsequently intervening in oocyte maturation and hydration, rendering heavier embryos. In Chapter 3, the visual acuity of larvae given either a DHA- or DHA+ diet was investigated at ages 0, 4, 8 and 16 days post hatch when the parents had been fed either a DHA- or a DHA+ diet for at least one month. This was accomplished by using an optokinetic response apparatus and exchangeable drums with black and white bands to create spatial frequencies of 6 to 30 cycles/360° at a mesopic light intensity of 5.0 lux and constant temporal frequency of 0.08247 Hz. Larvae from breeders given the DHA- diet showed their visual acuity improved when given the DHA+ diet after eight days of treatment (P≤0.05), and larvae from breeders given the DHA+ diet showed decreased visual acuity when raised on the DHA- diet after sixteen days of diet treatment (P≤0.06). Larvae from breeders given a DHA+ diet reached a low visual acuity of 7.46 cycles/360° after sixteen days of receiving a DHA- diet, a value similarly low to larvae given a DHA- diet from breeders given a DHA- diet (7.03 cycles/360°) after a similar period of time. Eye DHA% TFA day zero was greater in larvae given the DHA+ diet whose parents received a DHA+ diet than larvae given the DHA- diet whose parents received the DHA- diet. At day sixteen, DHA in larvae given the DHA- diet from breeders given the DHA- diet increased to a value (6.9% TFA) similar to the larvae given the DHA+ diet from breeders given the DHA+ diet (6.8% TFA). Their vision not only did not recover, but decreased by day sixteen.

Indexing (document details)
Advisor: German, J. Bruce
Commitee: Doroshov, Serge I., Klasing, Kirk C., Lanoue, Louise L.
School: University of California, Davis
Department: Nutritional Biology
School Location: United States -- California
Source: DAI-B 75/07(E), Dissertation Abstracts International
Subjects: Ophthalmology, Nutrition, Aquatic sciences
Keywords: Docosahexaenoic acid, Embryo weight, Fish growth, Fish larva vision, Fish reproduction, Omega 3 fatty acids
Publication Number: 3614268
ISBN: 978-1-303-79257-1
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