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Abstract

Fish oil (FO) is the major source of dietary lipid in carnivorous fish feeds including
barramundi, Lates calcarifer, which is widely farmed in Asia and Australia. However, recent
increases in FO prices, increased demand and the foreseen inability of wild fisheries to meet
future requirements have created a need for cheaper and more sustainable alternatives.
Vegetable oils (VO) can be produced in sufficient quantities to meet the growing aquaculture
demand, although they lack the long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA)
beneficial to human consumers. Some VO like rapeseed oil (RO), echium oil from Echium
plantagineum (EO) and linseed oil (LO) have high levels of n-3 and n-6 short-chain (≤C18)
PUFA that can accumulate or be converted into LC-PUFA by some fish species, although
generally at low efficiency, and not to docosahexaenoic acid. In a series of comparative and
factorial experiments, I investigated the growth and lipid changes of barramundi fed different
dietary oils: FO, RO, LO and EO over conditions covering: a range of salinities and
temperatures, subject to immunity stress or supplemented with plant-derived bioactive
ingredients. In general, growth performance parameters were comparable for FO and VO
treatments, and resulted in accumulation of VO-derived n-3 and n-6 PUFA. Salinity has no
direct effect on growth or lipid metabolism regardless of the dietary lipid source. Endogenous
conversion by barramundi of dietary PUFA into LC-PUFA is limited by more than one ratelimiting
step and there is a preference for incorporation of LC-PUFA into the polar lipid
fraction rather than neutral lipid. The growth of barramundi slowed at sub-optimal (20°C)
temperature compared to optimal (30°C) temperature. PUFA from dietary VO deposits in
muscle and are maintained under rapid temperature decreases. In contrast, excess LC-PUFA
from FO depleted faster than occurs in VO fed fish. The production of pro-inflammatory
eicosanoids in fish fed FO was lower than for fish fed VO following bacterial infection. EO
significantly suppressed the production of the pro-inflammatory mediators compared to RO.
Sesamin, a lignan in sesame seed, enhanced the conversion of dietary PUFA into LC-PUFA
for the n-3 series rather than n-6 in early juvenile barramundi. However, sesamin had
negative impact on fish growth at this early life-stage. Barramundi fed on VO are a rich
source of LC-PUFA precursors, α-linolenic and stearidonic acid, and grow well under the
different environmental conditions that are typical of outdoor barramundi farms. The use of
terrestrial VO containing the LC-PUFA precursors and plant-derived bioactive compounds
show promise for use in barramundi aquafeed in terms of fish growth and health as either
partial or complete alternatives for FO. However, using currently available VO, high content
of the n -3 LC-PUFA is not achieved.

Item Type:	Thesis - PhD
Authors/Creators:	Alhazzaa, R
Keywords:	Barramundi, fish oil, fatty acid, lipid nutrition, vegetable oil
Additional Information:	Copyright the Author
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