An international team of researchers from Canada and Iran examined the use of dietary arachidonic acid (ARA) on growth and reproduction in blue gourami. The researchers published their work in the journal Aquaculture.
“The present study investigated the effects of various amounts of dietary ARA on the growth, reproductive performance and the fatty acid composition of ovaries, fertilized eggs and 3-days post hatching larva of blue gourami (T. trichopterus) broodstock,” they said.
The group found that although it is an accepted idea that freshwater fish can convert short-chain poly-unsaturated fatty acids into longer-chain fatty acids, the bioconversion should not be assumed and some dietary supplementation may be needed, the researchers said. Adding ARA to the diet improved reproductive performance, though did not alter growth.
“Increasing ARA percentage in TFA [total fatty acids] of diet markedly influences the reproduction performance of blue gourami,” they said. “The results of this study confirm the importance of ARA in a freshwater tropical anabantid model fish.”
Why dietary ARA?
Factors including nutrition, environmental condition and age can alter the reproductive performance of fish used as broodstock, said researchers. The type and nature of essential fatty acids (EFA) are known to influence the reproductive process and development of the yolk sac and embryo.
Long-chain polyunsaturated fatty acid (LC-PUFA) levels in fish eggs and larval stages is influenced by the diet fed broodstock, they said. That interaction has been previously studied in several types of marine fish including red sea bream, yellowtail, yellow fin sea bream and certain freshwater species like channel catfih and nile tilapia.
“In earlier studies, the roles of LC-PUFAs such as DHA (docosahexaenoic acid; 22:6n − 3), EPA (eicosapentaenoic acid; 20:5n − 3), and ARA (arachidonic acid; 20:4n − 6) on different aspects of reproduction such as oocyte maturation, ovulation, fertility, spawning, hatching success and larval quality have been investigated in a few species,” the researchers said. “However, data on the importance of fatty acids in reproduction and sexual maturation in fish are limited and insufficient.”
ARA is long-chain fatty acid and a precursor of eicosanoids, which are involved in reproduction, they said. Past work, however, has focused on use of LC-PUFA DHA and EPA and little work has been done on the role of ARA.
Many marine fish need LC-PUFA in their feed, they said. “Despite the potential for the elongation and desaturation of long-chain fatty acids in freshwater fish, some recent studies highlighted the key role of this class of fatty acids (particularly ARA) in regulating physiological functions of reproduction,” they added.
However, there is some evidence that aging reduces the ability to synthesize LC-PUFAs and freshwater fish may not meet their full requirement for LC-PUFA through their diets, which may result in reproductive failure, they said. Supplementing diets with LC-PUFA appears essential.
It can be a challenge to evaluate the process and reproductive physiology of commercial broodstock fish, said the researchers. Blue gourami were picked for the study because it may be possible to make generalizations about similar teleost fish.
The species is a multi-batch spawner with an asynchronous ovarian development cycle, they said.
“The reason for selecting a multi-batch asynchronous spawning model is that these types of fish do not have sufficient time needed for the elongation and desaturation of short-chain fatty acids and subsequent transfer to their eggs,” they said. “It is, therefore, imperative to study the effects of EFAs in the diet of broodstock with asynchronous ovarian development.”
Methods and materials
In the study, 600 juvenile fish were given one of five diets supplemented with ARA for 150 days, said the researchers. The diets included 0, 0.5, 1. 1.5 and 2% ARA of total fatty acids.
A commercial product was used to add the ARA, they said. Diet ingredient were de-fatted and pelletized.
Sample fish were collected to establish weight, length, belly diameter and ovaries and livers were collected to establish gonadosomatic index (GSI) and hepatosomatic index (HSI), they said. Eggs were gathered to measure absolute and relative fecundities, oocyte and yok sac diameters and hatchability.
Growth parameters for the fish, including final weight, weight gain and specific growth rate, were similar for the different diets, said the researchers. But, the feed conversion ratio was lower for the control group compared to those getting diets with 0.5 or 1.5% added ARA.
Reproductive traits were altered by the amount of ARA in the diet, they said. The maximum relative and absolute fecundities were noted in the fish getting the diet with 2% ARA.
“These findings showed that T. trichopterus broodstock, as a model of asynchronous multi-batch spawning fish, needs to receive at least 1% ARA in their maturation diet to improve reproductive performance,” they said. “The best efficiency was achieved in 2% ARA, based on fecundity, yolk sac diameter and hatching rate.”
Fish getting the 1% ARA diet had the largest mean oocyte diameter, they said. The yolk sac diameter increased linearly along with the ratios of ARA to EPA and ARA to DHA as more of the supplement was added.
“Overall, the results of this study revealed the necessity of ARA inclusion in T. trichopterus broodstock diets,” the researchers said. “This conclusion challenges the generally accepted hypothesis that freshwater fish meet their highly unsaturated fatty acids (HUFA) requirements by elongation and desaturation their precursors.”
Title: The influence of dietary arachidonic acid on growth, reproductive performance, and fatty acid composition of ovary, egg and larvae in an anabantid model fish, Blue gourami (Trichopodus trichopterus; Pallas, 1770)
DOI: published online before print: 10.1016/j.aquaculture.2017.03.048
Authors: S. Asila, A. Kenaria, G. Miyanjib, G. Van Der Kraakc