Fatty Acid Profiles and Growth of African Catfish Larvae Fed on Freshwater Cyclopoid Copepods and Artemia as Live Starter Feed  

P. Chepkwemoi1 , Gladys Namuswe Bwanika1 , J. Kwetegyeka2 , G. Mbahizireki1 , L. Ndawula3 , A. A. Izaara4
1 Department of Biological Sciences, Makerere University, P.O. Box 7062, Kampala, Uganda
2 Department of Chemistry, Makerere University, P.O. Box 7062, Kampala, Uganda
3 National Fisheries Resources Research Institute, P.O. Box 43, Jinja Uganda
4 Mukono Zonal Agricultural Research and Development Institute, P.O. Box 164, Mukono, Uganda
Author    Correspondence author
International Journal of Aquaculture, 2013, Vol. 3, No. 22   doi: 10.5376/ija.2013.03.0022
Received: 26 Jun., 2013    Accepted: 05 Jul., 2013    Published: 22 Jul., 2013
© 2013 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Chepkwemoi, 2013, Fatty Acid Profiles and Growth of African Catfish Larvae Fed on Freshwater Cyclopoid Copepods and Artemia as Live Starter Feed, International Journal of Aquaculture, Vol.3, No.22 126-132 (doi: 10.5376/ija.2013. 03.0022)

Abstract

The possibility of utilizing freshwater crustaceans (Cyclopoid copepods) as an alternative live starter feed for African catfish (Clarias gariepinus, Burchell, 1822) larvae was explored. Larvae cultured in experimental tanks under ambient hatchery conditions were tested on three experimental diets for three days following commencement of exogenous feeding: freshly decapsulated Artemia cysts, early stages of Cyclopoids-copepods and a combination of the two. Change in total length measurements of larvae was used as a measure of growth. Fatty acid profiles of four-day old larvae were determined using Gas chromatography-mass spectrometry (GC-MS) method. Overall, growth of catfish larvae was significantly different (F=25.94, P<0.05) across diets. Cyclopoid-Artemia-fed larvae grew faster (9.1±0.89) mm, followed by Cyclopoid-fed larvae (8.8±0.92) mm and Artemia-fed larvae (8.6±0.79) mm. Similarly, significantly high composition of α linolenic acid (LNA), Arachidonic acid (AA), and Docosahexaenoic acid (DHA) were recorded for Cyclopoid copepods-fed larvae than for Artemia-fed larvae (LNA, F=14.7, P=0.028; AA, F=12.1, P=0.037 and DHA, F=101.9, P=0.002, respectively). These essential fatty acids play a significant role in the structural, physiological and functional development of larval fish thus promoting growth. A combination of Cyclopoid copepods with Artemia was of an added advantage possibly due to the large-sized Artemia that makes catchability easy. These results demonstrated that partial or total replacement of Artemia with Cyclopoid copepods as a live starter feed for African catfish larvae is feasible but call for further investigations on cost benefit analysis.

Keywords
Clarias gariepinnus; Larvae; Cyclopoid copepods; Artemia; Essential fatty acids; Starter diet

Aquaculture continues to expand worldwide to meet increasing human demand for fish following a decline in capture fisheries (FAO, 2008). The African catfish (Clarias gariepinus, Burchell, 1822) is a popular species for aquaculture in sub-Saharan Africa, and in Uganda, 60% of aquaculture production is owed to its culture (FAO, 2006). The African catfish, like other sensitive first-feeding larvae, faces considerable challenges in larval nutrition, (Cahu and Infante, 2001; Takeuchi, 2001; Infanteand Cahu, 2001). The larval stage is a critical stage in a fish’s life cycle that necessitates an appropriate exogenous nutrition once the embryonic yolk is used up. Larvae of most cultured species are generally poorly developed in physiological and morphological capacities incapacitating their use of manufactured feeds. As such, culture of appropriate and adequate quantities of live food is important in larval rearing of many aquaculture species (Whyte et al., 1989; Santiago et al., 1989). This stems from the fact that live foods do not only carry adequate supplies of macro-micronutrients, vitamins and sometimes antibiotics, but also provide a medium of enzymes that facilitates digestion (Lubzens, 1987).

The supply of shelf Brine shrimp (Artemia) cysts forms the basis of hatchery-based catfish seed production in Uganda. However, this does not go without challenges. The existing monopoly of this product on the market combined with costs associated with its importation into the country and unpredictable market supply impacts greatly on the costs of catfish seed production that makes it untenable for upcoming hatchery operators. Secondly, continual low survival rate (15%) of hatchery-based catfish seed has been attributed at least to some extent poor larval nutrition (Rutaisire, 2013, Personal communication, Aquaculture Research and Development Centre, Uganda) which implies that Artemia may not meet all the basic nutritional requirements of African catfish larvae. Globally, several reports indicate declining yield of Artemia cysts from the main wild source, the Great Salt Lake in Utah, USA, (Lavens and Sorgeloos, 2000). This trend, combined with likely climatic change impacts and increasing demand for aquaculture, necessitates deliberate efforts in mass production of alternative high quality live starter feeds for sustainable aquaculture development.
Research in marine fish larval nutrition is not new. Findings by Shields et al. (1999) indicated that Copepods provide better nutritional benefits to marine fish larvae than Artemia and Rotifers. The superior nutritional value of copepods has usually been attributed to their high polyunsaturated fatty acids (PUFA) and unsaturated fatty acids (HUFA) content essential to fish nutrition (Bell et al., 2003; Conceica et al., 2010). Molejo and Alvarez-Lajonchère (2003) therefore recommends culture of small pelagic copepod species using high-yield semi intensive technologies. Research on larval nutrition of freshwater larvae remains limited. Tocher (2010) argues that the initial assumption that freshwater fish are generally large enough to accept formulated feeds has hampered research initiatives in freshwater larval nutrition. It follows therefore that Information on the suitability of utilizing copepods as alternative starter live food in freshwater fish larvae is quite limited.
The present study compared fatty acid profiles and growth of African catfish larvae fed on freshwater Cyclopoid copepods and decapusulated Artemia in an attempt to present Cyclopoid copepods as alternative starter feed to Artemia, partially or in totality for the culture of African catfish larvae.
1 Results
1.1 Growth of Catfish Larvae Fed on Different Starter Diets
The impact of the three test diets on the growth of African catfish larvae was significantly different (F=25.94, P<0.05; Figure 1). Cyclopoid-Artemia-fed African Catfish larvae fed indicated best overall growth performance (9.1±0.89) mm followed by Cyclopoids-fed larvae (8.8±0.92) mm and Artemia (8.6±0.79) mm. A similar trend was observed for each day of feeding on the experimental diets.


Figure 1 Impact of test starter diets on growth of African catfish larvae

1
.2 Fatty Acid Profiles of Catfish Larvae Fed on Different Starter Diets
Variation in percentage composition of fatty acids of larvae fed on different starter diets was observed (Table 1). Palmitic acid (16:0) and stearic acid (18:0) were predominant among total saturated fatty acids (SFA) recorded for African catfish larvae fed on the different diets. Cyclopoid-fed larvae registered much lower total monounsaturated fatty acids (MUFA) (12.55±0.31)% as compared to Artemia-fed larvae and Cyclopoid-Artemia-fed larvae (21.30±0.3)% and (21.57±0.28)%, respectively). Oleic acid (18:1n9) and Vaccenic acid (18:1n7) were the most dominant MUFAs across diets. Composition of total polyunsaturated fatty acids (PUFA) was highest in Cyclopoid-fed larvae (45.83±0.38)% followed by Cyclopoid-Artemia-fed larvae (40.95±0.91)% and slightly lower in Artemia-fed larvae (37.85±2.14)%.


Table 1 Main fatty acid composition (% of total fatty acids) of catfish larvae fed on three experimental diets

Of the essential fatty acids, variation in composition was similarly observed across diets (Figure 2). Fish larvae fed on Cyclopoid copepods indicated significantly high percentage composition of docosahexaenoic acid (DHA, 22:6n3; F=101.9, P=0.002) and Arachidonic Acid (AA, 20:4n6; F=12.1 P=0.037). On the other hand, Artemia-fed larvae, had slightly higher levels of Linoleic Acid (LA, 6.5%) and Eicosapentaenoic Acid (EPA, 3.71%), than Cyclopoid copepod - fed larvae. Consequently, larvae fed on a combination of Artemia and copepods had significantly higher percentages of three of the essential fatty acids: Linoleic acid (LA, 18:2n6; F=24.1, P=0.014), Linolenic acid (LNA, 18:3n3; F=14.7, P=0.028) and Eicosapentaenoic acid (EPA, 20:5n3; F=96.3, P=0.002), and higher composition of all the five essential fatty acids when compared to Artemia only-fed larvae.


Figure 2 Impact of starter diet on essential fatty acid composition of African catfish larvae
 
2 Discussion
The superior growth performance of catfish larvae fed on a combination of Cyclopoid copepods and Artemia agrees well with previous studies that proved that inclusion of copepods in the early fish larval diets significantly improved survival and growth of fish larvae (Molejo and Alvarez-Lajonchère, 2003). This improvement in growth can be attributed to the nutritional base of Cyclopoid copepods as reflected in fatty acid profiles of catfish larvae fed on Cyclopoid copepods and a combination of Cyclopoid copepods and Artemia as when compared to the case of Artemia only fed larvae. According to Wetzel (1999), fatty acid composition of fish tissue is a consequence of the type of dietary lipid ingested and the ability of a given fish species to modify dietary lipids.
The predominance of PUFAs and SFAs as when compared to MUFAs across the test diets in this study, is in accordance with previous findings (Wiegand, 1996). Preferential catabolism of MUFAs along with preferential retention of DHA, EPA and AA, and specific SFAs, usually 16:0 or 18:0 by embryos of a variety of species has been recorded (Wiegand, 1996). This reflects the essential structural role of DHA in membranes, the importance of AA and EPA in eicosanoid production and specific roles of SFAs in the sn-1 position of structural phospholipids (Rainuzzo, 1993; Tocher, 2003).
In this study, total replacement of Artemia with Cyclopoid copepods conferred quantitatively higher composition of three (LNA, AA, DHA) of the five recorded essential fatty acids. Interestingly, partial replacement of Artemia with Cyclopoid copepods even yielded better results on all the five essential fatty acids. The ability of the Cyclopoid copepods like other herbivores, to convert linolenic acid (18:3n3) to eicosapentaenoic (EPA, 20:5n3) and consequently to docosahexaenoic (DHA, 22:6n3) acids (Norsker and Støttrup, 1994; Nanton and Castell, 1998; Desvilettes et al., 1997; Veloza et al., 2006) is a true reflection on the nutritional superiority of Cyclopoid copepods to Artemia. This observation is in accordance with other researchers who have indicated that copepods clearly outperform enriched rotifers and enriched Artemia in terms of meeting fish larval HUFA requirements (Bell et al., 2003; Evjemo et al.,2003; McKinnon et al.,2003; Olivotto et al., 2006; Conceica et al., 2010). Conceica et al. (2010) further argues that biovailability of HUFA in copepods is better than in Artemia because of the location of HUFAs in the phospholipid fraction in the former and in the neutral lipid fraction in the latter.
Docosahexaenoic acid (DHA) has important structural and functional roles in all membranes, but especially neural membranes (Feller, 2008; Wassell and Stillwell, 2008; Tocher, 2010) and a quite specific role in visual cell membranes, as in young developing mammals (Brett and Muller-Navarra, 1997). Fish larvae are thought to be visual feeders, adapted to attacking moving prey in nature (Conceica et al., 2010). Deprivation of DHA in larval herring (Clupea harengus L.) caused impaired visual performance, particularly at low light intensities when rod cells are active (Bell et al., 1995; Shields et al., 1999). Higher DHA content in cyclpoid copepod-fed larvae in this study could explain better growth due to improved visual performance of the larva leading to more larval feeding responses.
The high composition of AA in Cyclopoid copepod-fed catfish larvae in this study may further explain improved growth performance of catfish larvae as compared to when Artemia was used. Arachidonic acid (20:4n6; AA) is believed to be the chief source of eicosanoids in fish (Tocher, 2010). Eicosanoids produce highly bioactive molecules following regulated dioxygenase enzyme-catalysed oxidation of HUFA 20:4n6 (AA) and 20:5n3 (EPA). In fish, these molecules are involved in a great variety of physiological functions including blood clotting, immune and inflammatory responses, cardiovascular tone, renal and neural functions (Schmitz and Ecker, 2008).
A diet combination of Artemia with Cyclopoid copepods as a starter feed for African catfish in this study culminated into the best larval growth. The high composition of DHA and AA, the C22 and C20 metabolites of 18:3n-3 (LNA) and18:2n-6 (LA), respectively in Cyclopoid copepods is viewed as a booster that led to an increase in all the five essential fatty acids in the combination diet that led to overall improved growth. Of the essential fatty acids, LA and LNA are designated as true essential fatty acids for freshwater fish, because freshwater fish, are known to have an innate capacity to desaturate and elongate LA to 20:4n−6 (AA) and LNA to 20:5n−3 (EPA) and ultimately to 22:6n−3 (DHA) (Sargent et al., 2002). According to Sargent et al. (2002), a dietary source containing a combination of LNA, EPA, and DHA caused significant weight gain to milkfish (Chanos chanos). Although it is generally believed that freshwater/diadromous fish species require more of LA and LNA, while marine fish have a strict requirement for DHA, EPA and AA, larval organisms are thought to be more dependent on dietary HUFA than adults (Brett and Muller-Navarra, 1997; Vengadeshperumal et al., 2010) because the rate at which desaturation and elongation of LA and LNA may be too low to satisfy the growth demands of fast growing larval fish. Accordingly, Brett and Muller-Navarra (1997) recorded that various organisms with the ability to convert linolenic (LNA) acid to EPA and DHA grow better when provided with direct sources of EPA and DHA.
3 Conclusions
The dominance of SFAs 16:0 and 18:0; MUFAs 18:1n9 and 18:1n7 and PUFAs LA, LNA, AA, EPA and DHA in catfish larval tissue across all diets is an indication of a dietary requirement of these fatty acids in the diet of Catfish larvae. The consequential higher composition of the essential fatty acids and improved growth performance of catfish larvae fed on Cyclopoid copepods as compared to the case where Artemia is used indicates higher nutritional suitability of the former to the latter as a starter live feed for catfish larvae. Nevertheless, further investigation are required to assess the feasibility of mass culture of Cyclopoid copepods and associated cost effectiveness before more definite decisions are made on the partial or total replacement of Artemia with Cyclopoid copepods.
4 Methods and Materials
4.1 Culture of Cyclopoid Copepods
Zooplankton samples were collected using 45 μm mesh size plankton nets from grow-out fish ponds. Samples were coarse-screened through a 100 μm mesh followed by a 200 μm mesh for purposes of isolating a size fraction containing predominantly adult Cyclopoids and later-stage copepodites that were needed to initiate the culture. A subsample was taken and viewed under a microscope to ascertain presence of Cyclopoid copepods. On confirmation of presence of Cyclopoid copepods, Flubendazole was applied to the screened stock culture at a concentration of 0.5 mg/L for elimination of any remaining rotifers (Steenfeldt and Nielsen, 2010). Once a clean (95%) Cyclopoid copepod stock was achieved; cultures were initiated by hand picking and introducing at least 10 Cyclopoid copepods in each of 20 L plastic culture units using a micropipette. Twenty culture units were set up for the experiment and green micro algae (Chlorella species) that had been grown in parallel tanks used as a source of food. Cultures were maintained indoor at a room temperature range of 25-27, and illuminated daily for 12 hours using 40 watt electric lighting. pH remained at 6.5~9.0. Every 4~5 days, the cultures were renewed by descanting off 10 L of water through a 45 m screen from each 20 L culture unit and topping up with 10 L of green algae water. In order to avoid overcrowding that would lead to a culture crash, culture density of 10 L-1 Cyclopoid copepods was maintained by up scaling the culture whenever the set density was attained. Up scaling was achieved by dividing up the culture unit into two and topping up to 20 L using algae green water.
4.2Feeding Experiments Using Cyclopoids Copepods and Artemia as Starter Food for African Catfish Larvae
A commercial fish hatchery unit located in Ssenya fish farm, Masaka district, Uganda was utilized for the feeding experiment following the protocol outlined below:
(1) All water supplied to the hatchery was sieved through a 50 μm mesh to eliminate zooplankton contamination from the water supply ponds.
(2) Experimental plastic basins (30 L) were placed in triplicate in the hatchery unit for each of the three feed experimental set ups under investigation, modified to fit in the flow- through system of the hatchery unit.
(3) Catfish larvae were obtained by through artificial dissemination of catfish brood. Approximately 500 larvae were stocked in each of the 30 L experimental basins (16.6 larvae/L) and maintained under ambient hatchery conditions. Water temperature, dissolved oxygen levels, pH and ammonia levels were monitored and where required, necessary remedies were made.
(4) African catfish larvae were fed for three days on starter feed following commencement of exogenous feeding (day three) as is the practice of fish farmers in Uganda.
(5) The starter diets constituted three test diets namely: Decapsulated Artemia; Cyclopoids copepods; 50% decapsulated Artemia with 50% Cyclopoid copepods (nauplii and early copepoditie stages).
(6) Desired Cyclopoid copepods stages were obtained by coarse screening through 100 μm and 200 μm plankton nets. Decapsulation of Artemia cysts followed standard decapsulation procedures (Sorgeloos et al., 1977). Estimated of the required daily ratios (0.5 mL-1 -5.0 mL-1 Cyclopoid copepods and 1 mL-1-10 mL-1 Artemia cysts) was adopted, with slight modifications from Molejo and Alvarez-Lajonchère (2003). Fish larvae were fed five times a day in intervals of two hours and feed provided slightly above required estimates to allow feeding to satiation.
(7) Starting on day four to the sixth day, 30 larvae were randomly picked from each experimental basin one hour after the first feeding (9.00am) for measurement of total length (TL) as an indicator of growth. Each of the 30 larvae was placed on filter paper to allow absorption of excess water and for create a situation of inactivity before taking length measurements using a Vernier calliper.
(8) On the Seventh day, 30 fish larvae were scooped out of each experimental basin, excess water removed using filter paper, weighed using a sensitive analytical balance (nearest 0.0001g), packaged in aluminium foil and stored under ice before transporting the samples to the Department of Chemistry, Makerere University for subsequent fatty acid analysis.
4.3 Determination of Fatty Acids Composition
Fatty acid profiles of freshly collected fish larval samples were analysed following Joensen et al., (2000). Once the methyl esters were obtained from the samples, extracts were stored under refrigeration until Gas Chromatography-Mass Spectrometry (GC-MS) analysis using an Agilent 6890N GC-MS (USA version). The fatty acids in the samples were identified by means of the standard mixture GLC-68D from Nu-Chek-Prep (Elysian, Minn., USA) containing 20 fatty acids and by mass spectrometry. Quantification of the esters was achieved by integration of the peaks using Chemstation software obtained from Thermo LabSystems. The relative amount of each fatty acid ester in each sample was expressed as a percentage of all the esters in the sample.
4.4 Data Analysis
One-way ANOVA was used to compare growth performance of larvae fed on different diets and significant means compared using Tukey’s HSD test. The results obtained from the chromatography readings were presented as means±SD.
Acknowledgements
This research study was financed by the National Agricultural Research Organization through the Competitive Research Grant Scheme. The Department of Biological Sciences and Department of Chemistry of Makerere University, and the National Fisheries Resources Research Institute, Jinja, provided technical and logistical support. Special thanks go to Mr. Paul Sekyewa of Ssenya fish farm for availing us his hatchery unit and for his collaborative efforts. We also thank Ivan Abaho for his tireless assistance on the project.
Authors’ Contributions
GB, PC, AAI, GM and LN participated in the design of the study, cultured the Cyclopoid copepods, carried out the diet experiment on African catfish larvae, and fully participated in writing of this manuscript. JK analyzed fatty acid profiles and participated in the writing of the manuscript. PC and GB also provided extra input by analyzing the data and in supervising and coordinating the research activities.
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. Larvae
. Cyclopoid copepods
. Artemia
. Essential fatty acids
. Starter diet
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