The global production of tilapia exceeded three million tonnes in 2010 and is estimated by industry’s
forecast to increase to about nine million tonnes by the year 2020.
The increasing intensification of tilapia farming systems has led to a critical need for large quantities of fingerlings for stocking grow-out systems (see Figure 1).
Furthermore, it is increasingly important to produce high quality tilapia fry due to the low fecundity of broodfish, the low degree of female spawning synchrony and reduction in spawning rigor with time. Broodstock nutrition is recognised as a major factor that can influence fish repro-duction and subsequent larval quality of many fish species.
The development of cost-effective and nutrient optimised broodstock feeds for tilapia is both pertinent and crucial.
Tilapia broodstock nutritionLipids and fatty acids have been reported
to play a major role in broodstock nutrition and greatly influence the quality of develop-ing eggs and larvae.
Omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) such as eicosap-entaenoic acid (EPA, 20:5n-3) and docosa-hexaenoic acid (DHA, 22:6n-3), as well
as n-6 LC-PUFA such as arachidonic acid (ARA, 20:4n-6), are known to significantly influence reproductive performance in many farmed fish.
Marine fish oils are rich in LC-PUFA and are traditionally used as the major lipid source in aquafeeds, including broodstock feeds.
However, it is estimated that aquafeeds currently consume more than 90 percent
of the global supply of fish oil (FO) and the demand for FO from the expanding aquaculture industry will imminently out strip supply.
Considering the high demand, impending short supply and rising costs of FO, much research is currently being conducted on finding suitable alternative lipid sources for use in aquafeeds.
Vegetable oils are viable alternatives
Broodstock feedswith added crude palm oil enhances tilapia egg and larva production
by Wing–Keong Ng, PhD, Yan Wang, MSc, Yunyun Qian, MSc, Fish Nutrition Laboratory, School of Biological Sciences, Universiti Sains Malaysia, Penang, Malaysia Email: [email protected]
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F: Broodstock feeds
Figure 1: Red hybrid Tilapia fingerlings in a commercial hatchery ready for stocking grow-out culture systems
as they are readily available, renewal and more cost-effective compared to FO. Many studies have reported that vegetable oils can partially or fully replace FO in fish diets without compromising growth perform-ance as long as the essential fatty acid requirements of the fish are met.
However, all the major vegetable oils produced do not contain LC-PUFA in their fatty acid profile. Considering the reported importance of this group of fatty acids in broodstock nutrition, finding suitable lipid alternatives will be more challenging and requires concerted research effort.
There is currently very limited informa-tion on the effect of dietary vegetable oils and FO on the reproductive performance of tilapia.
Tilapia broodfish feeding trial
We recently conducted a feeding trial to evaluate the potential use of linseed oil and crude palm oil in tilapia broodstock feeds. Linseed oil (LSO) was chosen due to its very high concentra-tions of linolenic acid (18:3n-3). Previous research in our laboratory has indicated that Nile tilapia is capable of elongating and desaturating 18:3n-3 present in LSO to n-3 LC-PUFA.
We have also chosen to evaluate crude palm oil (CPO) as a potential lipid source.
In a previous study from our laboratory, tilapia, when fed CPO-based diets from stocking to marketable size was observed to have significantly larger gonads compared to fish fed the FO-based diet.
We therefore decided to conduct a comprehensive study to evaluate the effects of dietary lipid source (FO, LSO
and CPO) on the spawning perform-ance, egg and larval quality, and the fatty acid composition of various reproduc-tive products of Nile tilapia.
Experimental protocol
P re - s p aw n i n g female Nile tilapia, Oreochromis niloticus (GIFT strain), obtained from the same parental breeding pair was used. Before the start of the experi-ment, all female fish was individually color tagged (see Figure 2).
All male tilapia had their upper lip bone clipped to prevent injury to the female fish during mat-ing behavior. Two round one-tonne liter-breeding tanks were allocated for each group of fish fed their respective allocated diet.
Each tank was stocked with six female (mean initial weight, 31.9 ± 0.4g)
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F: Broodstock feeds
Figure 2: Pre-spawning female Nile Tilapia individually tagged with colour-coded disc tags tied to vinyl thread
Rising feedcost
Escalatingfish meal price
Opportunisticdiseases
Environmentalimpact
Low Shrimp& fish prices
Feed is the main cost in most aquaculture operations …
and the most difficult one to reduce when ingredient prices are rising …
mouth brooders, spawning fish also do not eat when they are mouth-incubating their eggs.
It is therefore not surprising that actively spawning female fish in the study showed lower growth performance. Broodfish fed the LSO diet which had the poorest repro-ductive performance showed the highest weight gain compared to fish fed the other three diets. In this study, tilapia fed the two CPO-based diets (CPO or FO+CPO) had larger gonads and less perivisceral fat, and combined with lower growth rates indicated that broodfish fed these two diets had increased reproductive potential and activity.
The significantly lower perivisceral fat found in broodfish fed the two CPO-based diets indicated the important contribution of the adipose tissue in providing fat and energy reserves during active reproduction. Perivisceral adipose tissue was less mobi-lized in broodfish fed the FO or LSO diet.
First spawning occurred earliest in broodfish fed the CPO diet at 30.8 ± 9.9 days compared to 44.1, 45.5 or 76.3 days for fish fed the FO+CPO, FO or LSO diet, respectively.
The highest number of actively spawn-ing tilapia was observed in fish fed the FO+CPO diet, followed by fish fed the CPO, FO or LSO diet, respectively.
At the end of 25 weeks, tilapia fed the two CPO-based diets produced the high-est total number of eggs per fish due to the shorter inter spawning interval, higher spawning frequency and and greater number of brooding females "(see Figure 5)". Mean diameter, volume and weight of eggs did not vary among dietary treatments.
Egg hatchability was significantly higher in broodfish fed the CPO-based diets.
It took three to four days for the incu-bated eggs to hatch, irrespective of diet. The
Impact on reproductive performance
During broodfish maturation and spawn-ing, much of the supply of dietary nutrients is channeled into the developing gonads, eggs and ovulation processes.
In the case of Nile tilapia, since they are
and two male (mean weight 41.3 ± 0.8g) tilapia, respectively.
Six rectangular plastic flower pots were placed on the tank bottom to provide breed-ing spaces for the spawning female tilapia. Fish were hand-fed to apparent satiation twice daily. Four isonitrogenous (35% protein) and isolipidic (10%) casein-based diets were formulated with added FO, FO+CPO (1:1), CPO or LSO as the lipid source, respectively.
Each diet was fed to two tanks of brood-fish and the reproductive performance of 12 individual female fish was monitored over 25 weeks.
Whenever present, eggs were gently removed from the buccal cavity of brooding fish and counted (see Figure 3).
Fish body weight and the date of spawning were recorded before return-ing the broodfish to their respective tank. Subsamples of eggs were randomly chosen and used either for egg biomet-ric measurements, fatty acid analyses or hatched in modified plastic bottles in a temperature controlled (28 ± 0.5 °C) indoor hatching system.
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F: Broodstock feeds
Figure 4: Tilapia fed 100% CPO diet spawned the earliest and had the shortest inter-spawning interval
Figure 3: Tilapia eggs are oval-shaped and both the long and short axis lengths were used for biometric measurements
gonad, egg and larvae of Nile tilapia was observed in this study. Vitamin E is known to be critical to the normal development of fish embryos and is therefore expected to have contrib-uted to the enhanced reproductive performance of Nile tilapia fed CPO-based diets in this study.
ConclusionIn conclusion, the inclusion of CPO in
tilapia broodstock diets can be a cost-effective method to increase tilapia fry production. The beneficial impact of die-tary CPO on female tilapia reproductive performance included larger gonad sizes, earlier first spawning activity, shorter inter-spawning interval, a longer period of broodfish fertility, higher overall total egg production, higher egg hatching rates and lower incidence of larval deformities as compared to broodfish fed a FO-based diet.
Authors’ note:The full report of this research
was recently published in Aquaculture (Ng and Wang, 2011. Aquaculture 314, 122-131).
The high total n-3 PUFA concentra-tion observed in the gonads of fish fed the LSO diet, and to a lesser degree the FO diet, seemed to be detrimental to the reproductive performance of tilapia.
One possible reason for the negative effects of excess n-3 LC PUFA might be due to the increased oxidative stress encountered by the gonadal tissues.
Highly unsaturated fatty acids are easily oxidized creating highly reactive lipid perox ida t ion radicals that might be det-rimental to the developing egg or embryo. R e p l a c i n g dietary FO with palm oil can improve oxidative sta-bility in fish tissues due to the more saturated fatty acid profile of palm oil and the presence of endog-enous vita-min E which are potent antioxidants.
A s i g -nificant accu-mulation of t o c o p h e ro l s and tocot-rienols in the muscle , l iver,
time taken for the yolk sac to be absorbed ranged from four to eight days. Larval morphology and survival after a stress test did not yield significantly different results among dietary treatments.
However, there was a significant increase in larval deformities observed in larvae from fish fed the FO diet
Fatty acids and fish reproduction
The fatty acid composition of the mus-cle, gonad, egg and newly hatched larvae was influenced by dietary lipid source.
However, evidence of preferential fatty acid conservation, conversion and utilisa-tion was also observed in these tissues. The fatty acid composition of tilapia eggs did not vary over four consecutive spawns.
The gonads and eggs of tilapia fed the CPO diet contained the highest rela-tive concentration of saturates, monoenes, arachidonic acid and n-6/n-3 ratio which all played a role in enhancing reproductive performance. The addition of CPO at the 50 percent or 100 percent replacement of FO greatly increased the dietary content of 16:0, thereby supplying more than sufficient levels of saturated fatty acids for optimal structural and functional roles in cellular membrane formation in the gonad.
The significantly increased monoene content provided the preferred substrates for mitochondrial β-oxidation for energy production in fish. High levels of monoenes are often accumulated in gonadal neutral lipids which are catabolised for energy after the eggs are hatched.
Arachidonic acid is the preferred sub-strate for prostaglandins production in fish cells and prostaglandins are known to be involved in the reproductive processes such as steroidogenesis and ovulation.
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