The various physio chemical parameters analysed during the culture trial was shown in Table 2 along with the statistical analysis. No significant difference was observed between the control and treatments for all the water quality parameters and were maintained at an optimal range throughout the experimental trial.
Zoo- technical performance of the shrimp post-larvae
No significant difference was observed in SGR for control, T1, T2 and T3 whereas control and T2 were found to be significantly different. Significant difference (P>0.05) in feed conversion ratio and survival rate were found between the experimental groups. Highest weight gain percentage was observed in T3. The growth performance of shrimp post-larvae was shown in Table 3. Shrimp post-larvae fed with enriched
Artemia exhibited enhanced growth and survival than control. Similar reports were observed by
Zelaya et al., (2007) who reported an improved growth performance in the diets of
L. vannamei supplemented with enriched fatty acids along with the commercial feed. This may be due to the increased fatty acid metabolism of the shrimp post-larvae leading to the faster growth rate
(Hurtado et al., 2007; Martins et al., 2006; Palacios et al., 2004b). The dietary requirements of essential fatty acids differ between penaeid species. The requirement of n-3 PUFA in
L. vannamei, P. Monodon and post-larval penaeid were found to be 0.5%, 0.5-1% and 1%
(Gonzalez-Felix et al., 2002; Chen and Tsai, 1986;
Kanazawa et al., 1979a). The lower growth rate in T4 compared to T3 may be due to the higher levels of dietary n-3 HUFA as reported in the studies of
Rees et al., (1994). The fattyacid supplementation >2% in the diet can lead to the declined growth performance and survival in
L. vannamei (Glencross and Smith, 2001). The increase in body weight and survival in T3 showed the better result in terms of feed conversion ratio and weight gain.
Fatty acid composition of Artemia franciscana
The fattyacid profile of the experimental diet reveals that higher levels of EPA (4.7%) were found in T4 than T3 (4.3%). The linoleic (18:2n-6) and linolenic acid (18:3n-3) levels in treatments were higher when compared to control. The fatty acid enriched with
Artemia nauplii affects the ån-3 HUFA levels ranging from 26.78% to 31.86% in treatments whereas in the control it was around <19.11% (Table 4). The total ether extract content of the experimental group ranges from 6.86% to 9.94%. The EPA/DHA ratio ranged from 12 to 28.66 in treatment groups. The recommended levels of EPA, DHA and other essential fatty acids were recorded in T1 and T2 as reported by Merican and Shim, 1997 in
L. vannamei and
Kanazawa et al., 1979b; Xu et al., 1993 in
Marsupenaeus japonicas and
Fraxinus chinensis. In the current study, the accumulation of saturated fatty acids was almost similar between the treatments. The fattyacid profile of the enriched and unenriched
Artemia nauplii revealed the absorption of fatty acid emulsions at different concentrations and absorption rate of nutrients were found in the inclined trend for the increased concentrations.
Fattyacid composition of shrimp post-larvae on 7th and 25th day sampling
On 7
th day, animals fed with enriched diet showed higher w-6 fatty acid accumulation in tissues and ån-3 HUFA ranged from 21.3 % to 25.07% whereas EPA/DHA ratios ranged from 1.297% to 2.612% (Table 5). On 25th day, w-6 fattyacid accumulation in tissues were same in T2 and T3 with ån-3 HUFA ranging from 14.38 % to 20.54% and EPA /DHA ratios ranging from 1.297% to 2.612% (Table 6). However due to the inherit capability of
Artemia sp., in DHA catabolism, EPA/DHA concentration was declining in the increased fatty acid concentration in the post-larvae on 7
thday. The fatty acid composition of the shrimp larvae on 7
th day was found higher at the increased concentrations which indicate the characteristic absorption of post-larvae. After a course of 7 days feeding of enriched
Artemia, the shrimp post-larvae were fed with commercial diet for 18 days. Interestingly, the fatty acid composition of the juveniles was higher up to 2% and absorption capacity of the shrimp juveniles were found lesser at 3% enrichment at the end of the trial. The retarding growth of the juveniles was found in T1 and T2 which might be due to the lack of adequate essential nutrients. The decline in growth rate of T4 compared to T3 might be due to the deposition of excessive fatty acid supplement leading to inhibition effect on the mRNA of fatty acid synthase (FAS)
(Chen et al., 2015). The findings of the present study revealed that
P. vannamei when fed with an excess HUFA do not enhance the growth of the animals and the utilization of short chain fatty acids were pronounced in all treatments in case of their deficiency, the animal prefer to use long chain fatty acids. Similar results were also found in the studies of
Deering et al., 1997; Palacios et al., 2004 who reported
P.monodon used shorter-chain fatty acids for their metabolism and were able to retain long-chain unsaturated fatty acids.
Histoarchitecture of the Hepatopancreas of P. vannamei
The numbers of hepatopancreas Basal cells (B cells) were higher in T4 than T3 but the size of the cells was normal. The normal architecture was observed with differential cells at each concentration. The interstitial sinuses between tubules were normal and in T4 well-organized glandular tubular structure were observed (Fig 1).
Histoarchitecture of the Intestine of P. vannamei
In the control group the epithelial cells and cellular structure of villi are columnar in shape, showing normal intestinal crypts, villi and laminar propria. The mean height of epithelial cells in abdominal segment was higher in T1, T3 and T4 than control. The shrimp mid-gut showed mild degeneration of intestinal epithelial cells (Fig 2).
Histoarchitecture of muscle
In T4, the muscle fibres displayed a variety of morphological changes of progressive myofibrillar degeneration and necroitic myopathy, due to deposition of heavy fats on the tissue (Fig 3).
No attempts were made till now to describe the histological changes of different tissues such as hepatopancreas, muscle and intestine of
P. vannamei reared in fatty acid enriched
artemia diet. The structure of hepatopancreas was normal in control however the number of B cells and R cells were significantly less in control. T1, T2, T3 and T4 groups tend to show the improved cellular architecture compared to control as the number of reserve cells (R- cells) was much higher. Similarly, in the present study it was found that different concentrations of fatty acids, reflected alterations in structure of epithelial cells and tubules of hepatopancreas. The number of R-cells was found in increased numbers in treatments than control which might be due to the high energy demand for osmoregulation which utilizes reserved nutrients from R-cells
(Li et al., 2008). This suggested that 3% fatty acid enriched diet has impact on the physiology in turn on the histological alterations in shrimp. The number of hepatopancreatic B-cells significantly increased in T2 and T3 compared to T4 with respect to the increased levels of EPA and DHA. Histological study of intestine is an important factor to be analysed as different morphological structure can be correlated with physiological functions such as digestion, assimilation and adaptation to varying salinity (Yamamoto and Hiraro, 1978;
Cataldi et al., 1998). The digestive tract of crustacean arises from an ectodermal stomodeum, an endodermal mesenteron and an ectodermal proctodeum (Vonk, 1960; Shiino, 1968; Johnson, 1980). Similarly, in the current experiment, alterations were observed in the height of epithelial cells. Those shrimps supplemented with fatty acid enriched diet showed best recovery in the structure of intestinal epithelial cells especially in T3 group which might be due to the persistence of higher levels of essential HUFA and EPA/DHA. Prominent changes in the muscle tissues underlying the exoskeleton were not seen between treatment and control fishes.
Therefore, from the histological findings it is suggested that the aquatic environment with 1%, 2% and 3% fatty acid enriched
Artemia feeding make tremendous changes in the organizational structure of hepatopancreas and intestine. Though the number of reserve cells and basal cells are high in 3% fatty acid (T4) enriched hepatopancreas tissue, the occurrence of myofibrillar degeneration in the muscles of the animals suggests the restriction of percentage enrichment up to 2%. Histologically, it is proved to enrich the
Artemia franciscana up to 2% of fatty acid for rearing the healthy shrimp post-larvae. Further, the study indicated that the enrichment of 2% fatty acid to
Artemia is highly beneficial to maintain the regular structure of hepatopancreas, muscle and intestine of shrimp post-larvae, which were also concurrent with the declined growth rate in the T4 restricting the growth performance.
