Evaluation of different diets to replace artemia nauplii for larval rearing of giant freshwater prawn (macrobrachium rosenbergii)

Nong Lam University, Ho Chi Minh City 35 Evaluation of different diets to replace Artemia nauplii for larval rearing of giant freshwater prawn (Macrobrachium rosenbergii) Nhan T. Dinh Department of Aquaculture Technology, Nong Lam University, Ho Chi Minh City, Vietnam ARTICLE INFO Research paper Received: April 02, 2018 Revised: May 23, 2018 Accepted: May 31, 2018 Keywords Artemia Artificial diet Larval rearing Macrobrachium rosenbergii Weaning Corresponding author Dinh The Nhan Email: dtnhan@hcmuaf.edu.vn ABSTRACT A study was conducted on Macrobrachium rosenbergii larvae to evaluate the efficiency of different diets to replace Artemia nauplii in the feeding scheme. The study included two experiments performed at pilot scale in 12–L tanks using a recirculating system. Larval stocking density was 100 larvae/L. After 7 days of feeding by Artemia nauplii, different diets, included wet and dry diets and decapsulated Artemia cysts, were tested to replace Artemia nauplii. An extra treatment using only decapsulated Artemia cysts throughout the complete larval rearing was also included. The results showed that feeding larvae exclusively decapsulated cysts for the complete rearing cycle was not appropriate. When gradually replacing up to 50% of the Artemia nauplii ration with wet or dry diets, good results in terms of growth, survival and quality of the larvae were obtained, similar to the control treatment receiving only Artemia nauplii. However, abruptly replacing 50% of the Artemia nauplii ration with artificial diets negatively affected larval development. Weaning could start from larval stage V, with about 25% of the Artemia nauplii replaced with artificial diet. Subsequently, the weaning ration could be increased up to 50% from stage IX to postlarva stage. Artificial diets should be provided in different particle size ranges based on the larval stage, gradually increasing from 250 to 1000 µm from stage V to postlarva stage. The results obtained in the present study may aid future research and serve as a baseline for further optimization of feeding strategies in prawn larviculture. Cited as: Dinh, N. T. (2018). Evaluation of different diets to replace Artemia nauplii for larval rearing of giant freshwater prawn (Macrobrachium rosenbergii). The Journal of Agriculture and Development 17(3), 35-43. 1. Introduction The giant freshwater prawn, Macrobrachium rosenbergii is a commercially important species in freshwater aquaculture in Vietnam and other Southeast Asian countries. Freshwater prawn farming has been pinpointed as one of the major target species of the aquaculture sector. The Min- istry of Fisheries of Vietnam has put forth that the annual production of M. rosenbergii must reach 50,000 tons utilizing 50,000 ha by the year 2025. The seed production demand of freshwater prawn will be of sufficient quality and quantity from 2 to 3 billion per year in 2025 to serve farm- ing (GOV, 2018). Freshwater prawn culture has great potential for rural aquaculture, generating considerable employment and income, thereby bringing prosperity to rural poor. Giant freshwa- ter prawn farming is environmentally sustainable, since it is practiced at lower grow–out density (New, 1995). A majority of seed used in grow out farming of M. rosenbergii comes from hatcheries (Murthy et al., 2004; Phuong et al., 2006). Ex- isting hatcheries in the country are however not producing up to their installed capacity due var- ious constraints. Artemia nauplii are the preferred live food source used in the larviculture of many crus- taceans of commercial value. Lavens et al. (2000) demonstrated that Artemia nauplii suffice to pro- www.jad.hcmuaf.edu.vn The Journal of Agriculture and Development 17(3) 36 Nong Lam University, Ho Chi Minh City duce M. rosenbergii postlarvae. However, others showed that Artemia nauplii do not completely fulfil the nutritional requirements of larvae dur- ing the last larval stages and therefore recom- mend the use of supplemental diets (Valenti & Daniels, 2000). As a feed source, decapsulated Artemia cysts have a higher energy and nutri- tional value than live Artemia nauplii (Bengtson et al., 1991). Leger et al. (1987) showed that de- capsulated Artemia embryos have 30–50% more energy than newly–hatched nauplii (instar I). Sorgeloos et al. (1977) suggested the use of decap- sulated cysts as a direct source for fish and crus- tacean larvae. Subsequent studies demonstrated that decapsulated cysts are a good feed similar to freshly hatched Artemia nauplii for the larvae of marine shrimps and freshwater prawn, such as Penaeus monodon (Mock et al., 1980), and Mac- robrachium rosenbergii (Bruggeman et al., 1980). Although live food such as Artemia nauplii has proven successful for raising the larvae of many species, inherent problems remain such as the po- tential introduction of pathogens into the culture system or the high costs of labour and equipment required for preparation. In addition, the nutri- tional quality and physical properties of Artemia nauplii are depending on the source and time of harvest of cysts (Sorgeloos et al., 1983). Im- ported Artemia cysts are predominantly used, which are expensive and uncertain in availabil- ity. Dependence entirely on Artemia as feed not only makes hatchery operations expensive, but also unsustainable (Murthy et al., 2008). The de- pendence on Artemia is also a major constraint in the expansion of Macrobrachium rosenbergii hatcheries (New, 1990). Hence, there is a need to look for acceptable alternative diets to re- place Artemia and reduce the cost of prawn lar- val rearing. Several alternative foods, both live and inert, are being investigated as either sup- plement or replacement for Artemia nauplii in crustacean hatcheries. Wan (1999) developed sev- eral semi–purified spray–dried diets and evalu- ated their performance with larval striped bass, Morone saxatilis and freshwater prawn Macro- brachium rosenbergii. Larvae of both species con- sumed the diets, but growth and survival were significantly less than that of Artemia–fed lar- vae. However, Kovalenko et al. (2002) reported that larval growth of freshwater prawn fed a mi- crobound diet was 90% of that achieved for larvae fed newly–hatched nauplii of Artemia. Survival of the larvae fed the microbound diet was not signif- icantly different from that of Artemia–fed larvae. Several studies also investigated supplementation of Artemia with prepared feed in prawn larval rearing (Sick & Beaty 1975; Corbin et al., 1983). However, no standard substitute for Artemia has been developed for freshwater prawn hatcheries. Barros & Valenti (2003a) developed an ingestion rate model of Artemia nauplii for M. rosenbergii larvae based on the individual ingestion rate and prey density. However, this equation indicated that Artemia is not an adequate prey for later larval stages and that there is a necessity for a supplementary diet from stage IX onwards. Sev- eral studies indeed confirm this finding, however controversy still exist concerning the best tim- ing to introduce formulated feeds in the feed- ing schedule. Daniels et al. (1992) recommend diet supplementation from stages V–VI. Barros & Valenti (2003b) reported supplementation should start from stage VII onwards. The development of the larval digestive tract and the increase of enzyme activity from stage VI onwards (Kumlu & Jones, 1995) may explain the acceptance of in- ert diets, since digestion processes become thor- oughly functional. In order to further optimize the feeding schedule for M. rosenbergii larval rearing, a series of experiments were performed in the present study to evaluate the use of for- mulated larval diets to supplement or partially replace Artemia nauplii. 2. Materials and Methods 2.1. Experimental animals Two experiments were conducted at the experi- mental hatchery of the Faculty of Fisheries, Nong Lam University, Vietnam. M. rosenbergii breed- ers bearing yellow eggs were obtained from cul- ture ponds in Ben Tre province, Southern Viet- nam and acclimated to the hatchery conditions for egg incubation. The water quality parame- ters of the broodstock tanks, photoperiod, and feeding were adjusted in accordance with the rec- ommendations for prawn rearing (New, 2003). In both experiments, the larvae were obtained from several oviparous female breeders to ensure that enough the quality larvae was supplied for the pilot scale experiments. Twenty four hours after hatching, larvae were collected and stocked into the experimental tanks. The Journal of Agriculture and Development 17(3) www.jad.hcmuaf.edu.vn Nong Lam University, Ho Chi Minh City 37 2.2. Experimental design Experiment 1 consisted of seven treatments, which originated from the combination of differ- ent diets (Artemia nauplii, decapsulated Artemia cysts, two commercial dry diets and a wet egg custard diet (Table 1). Experiment 1 was per- formed in pilot–scale 12–L cylindro–conical rear- ing tanks with three replicates per treatment. Three separate recirculation systems were in- stalled, with one replicate of each treatment as- signed to each system. Each recirculation system consisted of 120–L cylindro–conical reservoir tank connected to a 160–L submerged biological filter and a 60–L overhead tank. Water was continu- ously pumped from reservoir tank to the over- head tank and then forced back through the bot- tom of the rearing tanks by gravity at 0.3 L/min. An outlet screen (150 µm) at the surface of the rearing tank led the water back to the biolog- ical filter tank and at the same time retained the larvae and Artemia within the rearing tank. The filter screen was cleaned daily to avoid water overflow. Water with a salinity of 12 g/L was ob- tained through mixing deionised water (tap wa- ter source) and natural seawater. Aeration in the rearing tanks and filter tanks maintained the oxy- gen level above 5 mg/L. Ammonia, nitrite and nitrate were always below 0.1, 0.03 and 50 mg/L respectively, while pH varied from 7.8 to 8.2. The waste and uneaten food in rearing tanks were re- moved every morning before feeding by siphon- ing. The same amount of prepared water (mixed water) was added into the system to keep the wa- ter volume constant. Light was supplied for 12h per day at 800–1000 lx at the water surface. Lar- vae were stocked at an initial density of 50 lar- vae/L. Experiment 2 consisted of four treatments. In three treatments 25–50% of the Artemia nau- plii ration was replaced with different artificial diets based on the larval stage of the animals. A control treatment was fed 100% Artemia nau- plii (Table 2). Experiment 2 was performed in pilot–scale 12–L cylindro–conical rearing tanks with three replicates per treatment at initial lar- val density of 50 larvae/L using the same recircu- lation system and rearing condition as described in experiment 1. 2.3. Diet preparation and feeding M. rosenbergii larvae in the two experiments were fed different diets including Artemia fran- ciscana nauplii (Great Salt Lake strain, Crystal Brand, Ocean Star International, Inc. USA); a wet egg custard–like diet following the formu- lation of Hien et al. (2002); and two kinds of commercial shrimp larval diets (1) Brine Shrimp Flakes (Ocean Star International, Inc. USA) and (2) Gromate (Fantai company, Taiwan). The for- mulation of the wet diet and the proximate com- position of the three different substitution diets are presented in Table 3. Artemia naupllii were hatched according to standard techniques following Van Stappen (1996). Artemia nauplii were collected as instar I stage and kept in a refrigerator at 4–60C with gentle aeration in order to maintain instar I stage nauplii for feeding throughout the day. Decap- sulated Artemia cysts used in the experiment 1 were prepared following Tunsutapanich (1979). The ingredients of the wet diet were weighed and blended. The resulting mixture was placed in a pan and cooked in a water bath to pud- ding consistency. After cooling, it was cut into small pieces, individually wrapped with polyethy- lene film and kept in a freezer for use the next 1–2 weeks. Before being fed to the larvae, the pieces were made into smaller particles, which were then sieved with different mesh screens to obtain three size classes of 250–500, 500–750 and 750–1000 µm for feeding based on the larval stages IV–VI, VII–IX and X–XII respectively. The Brine Shrimp Flake diet was also sieved into different size classes using mesh screens to ob- tain the desired sizes for feeding. The Gromate feed had a particle size from 150–500 µm and could directly be fed to the larvae. All supple- mental or substitution diets were fed to the larvae from day 8 after hatching onwards (about larval stages V–VI). The artificial diets were fed several times daily following the feeding schemes in Ta- bles 1 and 2. The different substitution and sup- plementation treatments were based on a stan- dard Artemia ration of 6, 8 and 10 Artemia nauplii/mL/day for the periods from day 1–7; day 8–15 and day 16–PL stage respectively. The amount of formulated feeds given was based on visual observation of the larval tanks upon feed- ing. Special care was taken not to overfeed, as this may cause degradation of the water quality. 2.4. Evaluation parameters At day 10 and 15, a larval stage index (LSI) was determined following Maddox and Manzi (1976) www.jad.hcmuaf.edu.vn The Journal of Agriculture and Development 17(3) 38 Nong Lam University, Ho Chi Minh City Table 1. Different diets and feeding schedules used in experiment 1 Treatment1 Feeding scheme Day 1–7 Day 8–PL 7h 17h 7h 9h 10h 11h 12h 13h 14h 15h 17h 100N 50N 50N 50N 50N 50N+50C 50N 50N 50C 50N 100C 50N 50N 50C 50C 75N+F 50N 50N 25N F F F 50N 75N+W 50N 50N 25N W W W 50N 50N+F 50N 50N F F F F F 50N 50N+W 50N 50N W W W W W 50N 1N: Artemia nauplii; C: Decapsulated Artemia cysts F: Brine Shrimp Flakes; W: Wet diet. Values rep- resent the percentage of the standard daily Artemia nauplii/cysts ration, which constitutes 6, 8 and 10 Artemia nauplii/cysts/mL for day 1–7; day 8–15 and day 16–PL stage respectively. Table 2. Different artificial diets and feeding schedules used to supplement or substitute Artemia nauplii in experiment 2 Treatment1 Larval rearing day Feeding scheme 7h00 10h00 12h00 14h00 17h00 Control treatment (1) 100N 1–PL 50N 50N Replaced Artemia treatments was applied the same feeding regime in below (2) N+W; (3) N+F; (4) N+G 1–7 50N 50N 8–15 25N x x x 50N 16–PL x x x x 50N 1N: Artemia nauplii; W: Wet diet; F: Brine Shrimp Flake; G: Gromate; “x”: time points when artificial diet was fed. Values represent the percentage of the standard daily Artemia nauplii ration, which constitutes 6, 8 and 10 Artemia nauplii/mL for day 1–7; day 8–15 and day 16–PL stage respectively. to assess larval development. (LSI was deter- mined during larval stage from 1-11 when has not any PL occurred). For this at least 30 lar- vae were sampled from each treatment and the average larval stage determined. The larval stage was recorded based on the description by Uno and Kwon (1969). The duration of the rearing cycle (days) was determined for each rearing tank. For this the duration from larval stocking up to the time 90% of the larvae in the rearing tank had metamorphosed into postlarvae was recorded. At the same time the final larval survival rate in each treatment was recorded. Larvae were also sub- jected to a total ammonia nitrogen (TAN) tox- icity test following the procedure described by Armstrong et al. (1978) in order to assess larval quality. Where: [NH3] = [TAN] / (1 + 10[pK–pH]) pK = 9.31 at temperature of 280C and salinity of 12 g/L. pH = mean of values measured at the begin- ning and the end of test. The test was performed on postlarvae in a se- ries of 1–L glass cones at 28±10C. Groups of 30 animals from each treatment were exposed during 24h to 4 increasing concentrations of total ammo- nia and a control (no ammonia added). As the toxicity of TAN is a function of temperature and pH, the pH of the test solution was adjusted at 7.8–8.0. Based on the mortality rates, the mean lethal concentrations for 50% of the population (24h–LC50) were estimated. 2.5. Statistical analyses Larval stage index; duration of rearing cy- cle; survival and ammonia toxicity data were analyzed by analysis of variance (one–way ANOVA) and, if significant differences were found (P < 0.05), the least significant dif- ferences (Weller–Duncan) test was applied for post hoc comparison. All percentage data were normalized by square root–arcsine, but only non–transformed means are presented. The Journal of Agriculture and Development 17(3) www.jad.hcmuaf.edu.vn Nong Lam University, Ho Chi Minh City 39 Table 3. Formulation of the wet diet and proximate composition of the three formulated diets Formulation of wet diet (%) Proximate composition of formulated diets (% dry weight) Wet diet Flakes* Gromate* Milk powder 53.8 Protein 48.6±1.2 53 57 Chicken egg yolk 41.7 Lipid 25.5±0.7 9 8 Squid oil 3.0 Ash 5.8±0.1 4 13 Lecithin 1.5 Mineral 6.5±0.1 2 2 Vitamin C 200 mg/kg Fiber 0.3±0.0 2 4 Moisture 57.7±2.5 9 9 *Composition based on the product label. 3. Results 3.1. Experiment 1 Larval development rate in terms of larval stage index in experiment 1 showed significant differ- ences between treatments. At day 10, three dif- ferent groups had formed based on larval stage index (P < 0.05). The lowest performance was observed in the treatments 50N+50C and 100C. In contrast to the fastest growth was found for treatments 100N, 75N+F and 75N+W. Treat- ments 50N+F and 50N+W showed intermedi- ate development rates. At day 15 of the ex- periment, the larval development rate in treat- ment 100C was significantly lower compared to all others treatments (P < 0.05). The treatment 50N+50C had a significantly higher LSI than the treatment 100C but lower than treatment 75N+W (Figure 1). Larval survival rate at the end of rearing cycle also showed significant dif- ferences. Three different groups could be distin- guished. The lowest survival (30%) was observed in the treatments 100C and 50N+F. The high- est survival (43–45%) was observed in the treat- ments 100N, 75N+F and 75N+W. Intermediate values around 35% were found in the treatments 50N+50C and 50N+W (Figure 2). Considering the duration of the rearing cycle, an opposite trend as for survival was noted. Larvae in the treatments 75N+F and 75N+W needed around 24–25 days of rearing to reach the postlarval stage, which was significantly shorter than for treatments 50N+50C and 100C, in which the du- ration of the rearing cycle was extended up to 28–29 days (Figure 2). The results of the ammo- nia stress test showed differences in postlarval tol- erance (LC50) (P < 0.05). The group containing treatments 100C and 75N+F presented the lowest values (136–138 mg/L TAN), intermediate toler- ance levels were found in treatments 50N+50C and 50N+W (165–168 mg/L TAN), while the highest tolerance was found in treatments 75N+F and 75N+W (185–189 mg/L TAN) (Figure 3). In general, the treatments 100N, 75N+W and 75N+F showed the best overall results in term of larval development, survival and larval quality. While the treatments 100C and 50N+F showed the lowest results. Figure 1. Larval stage index at day 10 and 15 ofM. rosenbergii larvae reared according to different feed- ing schedules in experiment 1. Different letters be- tween treatments denote significant differences (P < 0.05). For description of treatments refer to Table 1. 3.2. Experiment 2 At day 10 of the rearing period, the larvae in the different treatments showed the same devel- opment rate (P > 0.05). However, larval devel- opment rate in treatments 100N and N+W be- came significantly higher compared to treatment N+G (P < 0.05) by day 15 of the rearing cy- cle (Figure 4). Survival rate results at the end of the experiment revealed a significantly higher survival in treatments 100N and N+W (53–54%) compared to treatment N+G, which had a sur- vival of only 40% (P < 0.05). Evaluation of the www.jad.hcmuaf.edu.vn The Journal of Agriculture and Development 17(3) 40 Nong Lam University, Ho Chi Minh City Figure 2. Survival and duration of the rearing cycle of M. rosenbergii larvae reared according to different feeding schedules in experiment 1. Different letters between treatments denote significant differences (P < 0.05). For treatment descriptions refer to Table 1. Figure 3. Ammonia tolerance (expressed as 24 hour LC50–TAN) of M. rosenbergii larvae reared according to different feeding schedules in experiment 1. Differ- ent letters between treatments denote significant dif- ferences (P < 0.05). For treatment descriptions refer to Table 1. duration of rearing cycle showed that larvae in the treatment N+W completed the rearing cycle in 25 days, which was significantly shorter than in the treatments N+F and N+G which needed 28 and 29 days respectively (Figure 5). Postlar- val tolerance to total ammonia was significantly higher in treatments 100N and N+W (190 and 214 mg/L TAN respectively), compared to treat- ment N+G for which the LC50 was only 145 mg/L TAN (P < 0.05) (Figure 6). In general, the treat- ments 100N and N+W showed better results in terms of larval development, survival, rearing and larval quality compared to treatment N+G. 4. Discussion In experiment 1, the results of larval devel- opment, survival, duration of the rearing cycle and larval quality distributed the treatments into three distinct groups. The best group included the treatments fed exclusively Artemia nauplii and the treatments in which around 25% of the Figure 4. Larval stage index at day 10 and 15 of M. rosenbergii larvae reared according to different feed- ing schedules in experiment 2. Different letters be- tween treatments denote significant differences (P < 0.05). For treatment descriptions refer to Table 2 and 3. Figure 5. Survival and rearing cycle of M. rosen- bergii larvae reared according to different feeding schedules in the experiment 2. Different letters be- tween treatments denote significant differences (P < 0.05). For treatment descriptions refer to Table 2 and 3. Artemia ration was replaced with artificial wet or dry diets. Consequently, the replacement of a part of the live food in the feeding schedule did not affect performance of the larvae. However, treatments in which 50% of the live feed was re- placed from day 8 onwards reduced survival rate and larval quality. Especially, the use of an exclu- sive diet of decapsulated Artemia cysts seemed not appropriate for M. rosenbergii larval devel- opment. Although Artemia cysts are reported to contain higher energy and nutrient levels than Artemia nauplii (Sorgeloos et al., 1977; Leger et al., 1987; Bengtson et al., 1991), it was observed that they rapidly sink to the bottom upon feed- ing, thus reducing their availability for the lar- vae to feed upon in the water column (Lavens & Sorgeloos, 1996). This while the behavior of prawn larvae is rather to swim in the upper part of the water column or at the water surface. In- creasing the aeration in the rearing containers may keep these particles better in suspension, however the increased turbulence may make it The Journal of Agriculture and Development 17(3) www.jad.hcmuaf.edu.vn Nong Lam University, Ho Chi Minh City 41 Figure 6. Ammonia tolerance (expressed as 24hour LC50–TAN) of M. rosenbergii larvae reared according to different feeding schedules in experiment 2. Differ- ent letters between treatments denote significant dif- ferences (P < 0.05). For treatment descriptions refer to Table 2 and 3. more difficult for the larvae to capture and in- gest the prey. Decapods larvae do not specifically orientate towards a food source, they depend on chance encounter to capture food (Kurmaly et al., 1989). In addition, Artemia cysts have a round shape, which may be difficult for the larvae to capture and hold on to during eating. In contrast, the mobility of Artemia nauplii allows its perma- nence in the water column, thus, increasing the chances of encounter (Barros & Valenti, 2003a). Using exclusively decapsulated cysts, which have a narrow size range (210–260 µm, Tackaert et al., 1987) may also not be appropriate for all lar- val stages during development. Barros & Valenti (2003a) suggested that live food supplementation should start from stage VII onwards, using food particles increasing from 250 to 1190 µm. There- fore, the dimensions of decapsulated cysts may be appropriate for stage VII and VIII M. rosenbergii larvae only. Replacing Artemia nauplii by artificial diets at a constant ratio of 50% from larval stage V–VI onwards (in experiment 1) negatively affected survival rate, but did not affect larval growth. This may be explaining by the drastic and sud- den reduction of live feed in these treatments. In these treatments live feed was supplied only one time per day in the evening, and consequently the live feed density during the day time was low. Es- pecially in the early period of weaning, the lar- vae may not have been adapted yet to non–living feed, probably resulting in low survival due to increased cannibalism. Indeed, when the larvae were more gradually weaned from Artemia onto formulated feeds (experiment 2), better results were obtained. Therefore, it is recommended to replace only 25% of the Artemia ration at the start of the weaning period to allow the larvae to adapt to the new diet. Subsequently, the weaning ration may be increased up to 50%, spread over several feedings per day. The replacement diets need to be offered with increasing particle sizes in function of the larval stage. In this respect, it was found that the Gromate feed, which had a rather narrow particle size range of 150–500 µm showed lower results compared to the wet and flake diets. Although the Gromate feed contained a higher protein level than the other diets, the narrow particle size range may have been a dis- advantage for later M. rosenbergii larval stages. In contrast, the wet and flake diet could easily be sieved into the desired particle sizes using sieves with different mesh sizes. In the present study, artificial diets were sup- plied from day 8 (stage V–VI) onwards. It was noticed that the larvae readily accepted the in- ert feeds. In this respect, the wet diet seemed to be more attractive to the larvae than the dry diets. Barros & Valenti (2003a) stated that the larvae only accepted inert feed from stage VII onwards and suggested that the live feed could totally be replaced with wet or dry diets from stages VII and IX onwards respectively. How- ever, it is necessary to evaluate final survival rates and productivity when applying total sub- stitution of Artemia for commercial larviculture. Murthy et al., (2008) suggested that using wet diets which contain shrimp and clam meat fed to larvae in combination with Artemia nauplii showed larval survival rates of 40% in 150–l rear- ing tanks. Islam et al. (2000) reported that fresh- water prawn larvae reared in a recirculation sys- tem with 140–l rearing tanks fed Artemia nau- plii supplemented with egg custard obtained a survival of 30%, which was higher than larvae fed exclusive Artemia (only 12%). However, Ka- marudin et al. (2002) studied the use of artifi- cial diets containing various ratios of cod liver and corn oil to replace 25-100% of the stan- dard Artemia nauplii ration from stage III to XI. The results showed that there were no significant differences in survival between the substitution treatments and the control treatment fed solely Artemia nauplii. In the current study, a gradual replacement of up to 50% of the Artemia nau- plii ration with wet and dry diets showed similar compared to a 100% Artemia control in terms of larval development, survival and larval qual- www.jad.hcmuaf.edu.vn The Journal of Agriculture and Development 17(3) 42 Nong Lam University, Ho Chi Minh City ity. However, performance was impaired when the Artemia diet was abruptly replaced at a con- stant rate of 50% from day 8 onwards. In practice production efficiency depends on the production cost, which is based on the feed source and cost, labour cost, etc., cost–effectiveness may there- fore vary from one region to another. Therefore, the feeding strategy in M. rosenbergii larviculture cannot be standardized. The results obtained in the present work may however serve as a guideline for practical considerations of feeding strategies. References Armstrong, D. A., Chippendale, D., Knight, A. W., & Colt, J. E. (1978). 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