ORIGINAL

Effects of different dietary of protein and lipid levels on the growth of freshwater prawns (Macrobrachium carcinus) broodstock

Efecto de diferentes niveles dietéticos de proteína y lípidos en el crecimiento de reproductores del langostino de agua dulce (Macrobrachium carcinus)

Mario Benítez-Mandujano,¹ M.Sc, Jesús T. Ponce-Palafox,²* Ph.D.

¹Universidad Juárez Autónoma de Tabasco, División Académica Multidisciplinaria de los Ríos, Laboratorio de Acuacultura. Carretera a Estapilla km. 1 Col. Solidaridad. Tenosique, Tabasco 86900. México.
²Universidad Autónoma de Nayarit, Escuela Nacional de Ingeniería Pesquera y Centro de Innovación y Transferencia Tecnológica (CENITT). Tepic, Nayarit 63155. México.

*Correspondencia: jesus.ponce@usa.net

Received: February 2013; Accepted: August 2013.

Objective. Evaluate the effects of varying dietary protein and lipid levels on the growth and body composition of adult freshwater prawns, Macrobrachium carcinus (Linnaeus 1758), in a recirculation system for 11 weeks (77 days). Materials and methods. The experimental treatments were assigned in triplicate. Six test diets were formulated with three different protein levels (35, 40 and 45%) and two lipid levels (8 and 13%). Results. The highest survival rate, growth indices and feed utilization were observed for M. carcinus adults fed protein:lipid diets of 35:13, 40:13 and 45:13, and the lowest values for these parameters were recorded for prawns fed diets with the lowest lipid levels; the differences in these parameters between these types of diets were significant (p<0.05). A non-significant tendency for an increased percentage of protein in the body with an increased dietary protein level was observed. The percentage of lipids decreased with an increasing dietary protein level, and no definite trends in ash content were found. Conclusions. The results suggest that a diet with 35% dietary crude protein and 13% lipids enhances the growth and body composition of adult M. carcinus.

Key words: Diets, growth, Macrobrachium, nutrition (Source: CAB).

RESUMEN

Objetivo. Evaluar los efectos de diversos niveles dietéticos de proteína y lípidos en el crecimiento y composición corporal de reproductores del langostino de agua dulce Macrobrachium carcinus (Linnaeus 1758), en un sistema de recirculación durante 11 semanas (77 días). Materiales y métodos. Los tratamientos experimentales fueron asignados por triplicado. Seis dietas de prueba fueron formuladas con tres niveles diferentes de proteínas (35, 40 y 45%) y dos niveles de lípidos (8 y 13%). Resultados. Se observó la tasa más alta de supervivencia, índices de crecimiento y utilización del alimento para ejemplares adultos de M. carcinus alimentados con niveles dietarios de proteína: lípidos de 35:13, 40:13 y 45:13, mientras que el valor más bajo en estos parámetros se registró en langostinos alimentados con el nivel más bajo de lípidos; las diferencias en estos parámetros entre estos tipos de dietas fueron significativas (p<0.05). Se observó una tendencia no significativa en un aumento del porcentaje de proteína en el cuerpo con un nivel mayor de proteína dietética. El porcentaje de lípidos disminuyó con un nivel de proteína dietario creciente, y no se encontró ninguna tendencia definida en el contenido de cenizas. Conclusiones. Los resultados sugieren que una combinación de dieta de proteína cruda del 35% y 13% de lípidos mejora el crecimiento y composición corporal de M. carcinus adultos.

Palabras clave: Crecimiento, dietas, Macrobrachium, nutrición (Fuente: CAB).

The freshwater prawn Macrobrachium carcinus, one of the largest American palaemonids, lives in fresh and brackish waters of eastern North, Central and South America (Florida to southern Brazil) and the West Indies (1). The species is an important local source of protein for human consumption along the Atlantic Ocean in Latin America. Though M. carcinus adults live and breed mainly in fresh water, larval development occurs only in brackish water. This is a species of commercial interest that has been exploited by the fishery industry in several countries. Studies of the suitability of this species for aquaculture purposes have reported the possibility of artificially cultivating and successful rearing the larvae through the juvenile stage (2).

Food is one of the most important factors affecting the growth, feed conversion and carcass composition of freshwater prawns (3). Prawns in all stages of development feed upon both animal and vegetable material, including aquatic insects, fish, mollusks, other crustaceans, algae, leaves and stems of aquatic plants and plant seeds of various types (2). A slight preference for animal food is observable in prawns above 26 mm in total length.

Freshwater prawns are considered a delicacy and are therefore in high demand in domestic and foreign markets. They are well known as a high-protein and low-fat food, containing 16-19% protein, 1.0-2.2% total lipids and 85-90 kcal of gross energy (2). Investigations into their feeding habits and food preferences suggest that M. carcinus larvae prefer live, mobile food, in this case the nauplii of Artemia salina (2). A few studies have been carried out on juvenile M. carcinus nutrition and feeding (1). M. carcinus adults were fed camaronina pellets (Purina K-35) containing 35% protein. In the Malaysian prawn M. rosenbergii, the adult diet influences both the size and biochemical composition of the eggs (4). Diets differing in protein content affect the quality of eggs produced by adults of both M. rosenbergii and M. tenellum (4). The aim of this study was to determine the effects of increased protein in the diet of M. carcinus adults to better assess their growth and nutritional quality.

MATERIALS AND METHODS

Experimental diets. The ingredients and nutrient content of each experimental diet are shown in table 1. Six experimental diets were formulated with various dietary protein levels (35, 40 and 45%) and dietary lipid levels (8 and 13%). All dry ingredients were finely ground, carefully weighed and manually mixed. Fish oil was then added slowly while mixing continuously, and water (25-30%, v/w) was then added to achieve a homogenous mixture. The feed mix was then passed through a screw extrusion press with a 2.5 mm-diameter die. Feed pellets produced for each experimental diet were air dried and stored at -15°C until use.

Prawn and experimental design. Adult M. carcinus were caught in the Usumacinta River in front of the town of El Recreo (17° 28.53' N, 91° 25.68' W) in the municipality of Tenosique, Tabasco, Mexico. The animals were transported to the Aquaculture Laboratory of the Multidisciplinary Academic Division, Juárez Autonomous University of Tabasco, Mexico. They were acclimated to laboratory conditions for 15 days and fed a commercial diet containing 35% protein before beginning the 77-day experiment. Eighteen males and 36 females were randomly allocated to 18 circular plastic tanks (1000 L capacity). Each tank had an operating volume of 345 L in a 1.54 m2 area and represented a single treatment group that housed one male (205.0±87.2 g) and two females (68.6±17.3 g). Pieces of PVC pipe (30 cm long and 6 cm in diameter) were placed in each tank to serve as refuges for the prawns. The tanks were maintained by a continuous recirculation system (2%) via a 3/4 Hp pump (Siemens N, DF, Mexico) that generated a daily turnover volume of 300%; a 1/3 Hp blower (Pioneer, RB20-510, Ling-Ya, Kaohsiung, Taiwan) aerated the water, and a sand filter (ms HAYWARD 180T New Jersey, USA) provided mechanical filtration. During the experiment, prawns were exposed to a 12:12 L:D photoperiod.

The experimental design was bifactorial, with three replicates per treatment: dietary protein level (35, 40 and 45%) was designated the first factor, and dietary lipid level (8% and 13%) was the second factor. The prawns were fed an experimental diet to satiety (determined visually) twice daily (at 8:00 and 18:00 hours) for 11 weeks. Dead juveniles and uneaten food were removed daily and weighed. The amount of food provided was later adjusted.

The water was continuously aerated. Recirculated tank water was tested daily at 10:00 hours for the following parameters: water temperature (°C), dissolved oxygen (mg/L DO), pH, alkalinity (mg/L) and ammonia nitrogen (N-NH₄) using a ATAGO salt-meter (salinity ± 0.05% precision); YSI-58-meter, Ohio, Springfield, USA (°C±0.7; DO±0.1 mg/L precision); pH-meter Orion Abilene, TX, USA (pH±0.01); and multiparameter meter (Hanna C200, Hungary).

Growth rates and chemical analysis. Group weight, individual weight (g) and total length (mm) were recorded for each prawn at the end of the study. At the end of the growth trial, all prawns were weighed and counted. Mean daily weight gain (MDWG, g/d) was calculated as MDWG = (Wf - Wi)/t. Specific growth rate (SGR, % body weight/d) was calculated as:
SGR = 100 X (ln Wf - Ln Wi)/t, where ln=natural log, Wf= mean weight at the end of the culture period, Wi= mean weight at the beginning of the experiment, and t=time in days of the experimental period (5). At the end of the feeding trial, the food conversion ratio (FCR) was calculated as FCR=(W feed consumed)/(W wet weight gained); the protein efficiency ratio (PER) was calculated as PER=(weight gain, g)/(protein intake, g); and the lipid efficiency ratio (LER) was calculated as LER = (weight gain, g)/(lipid intake, g). Survival was calculated on the basis of the number of freshwater prawn harvested: survival = [(number of prawn harvested)/(number stocked)] x 100) per tank (5).

After acclimatization, fifteen prawns were sampled and stored at -75°C for subsequent analysis of the tail muscle composition. At the end of the study, the prawns in each treatment were analyzed regarding the chemical composition of the tail muscle following the methods of the Association of Official Analytical Chemists (6). Crude protein (N x 6.25) was determined by the Kjeldahl method after an acid digestion using an Auto Kjeldahl System (2100-Auto-analyzer, Tecator, Hoganas, Sweden), and crude lipid content was determined by ether extraction. Crude lipid content was quantified by an automatic analyzer (Fibertec, Tecator). Nitrogen-free extract (NFE) was determined by calculating the difference.

Statistical analysis. All data are presented as the mean of three replicates. Data were subjected to a two-way ANOVA (7), and the significance level was set at p<0.05. Tukey's multiple range test was used to rank groups when statistical significance was achieved. Statistical analysis was performed using the STATISTICA program Version 7.0 for Windows (STATISTICA Stat Soft, Inc. 2004, USA).

RESULTS

The study was conducted indoors at 28.0±1.0°C, DO 6.5±0.8 mg/L, pH 7.5±0.4, N-NH₄ 0.24±0.2 mg/L and alkalinity 170±5.1 mg/L. Over the duration of this study, no significant differences were observed in water quality indices between the experimental treatments.

The proximate composition of the experimental diets is shown in table 1. The total dietary protein ranged from 35.0 to 45.3%, total lipids ranged from 7.9 to 13.2%, carbohydrates ranged from 19.2 to 35.4 % and gross energy ranged from 19.4 to 19.9 MJ/kg diet. During the investigation, the water stabilities of the experimental diets were between 4.0 and 5.0 h.

Growth performance. Growth performance and the associated nutritional indices are presented in table 2. Survival for the freshwater prawn varied between 83.2% and 100.0%, and significant dietary effects were observed (p<0.05). Survival was highest among prawns fed a diet with a P:L ratio of 45:13 and lowest for the diet with a P:L ratio of 40:8. Final body weight, WG, SGR and FCR are shown in table 2. Although growth occurred across all treatments, prawns fed diets with 8% lipids exhibited slower growth that those given 13% lipids. Both average daily weight gain and specific growth rate differed significantly among the experimental diets (p<0.05); diets with P:L ratios of 35:13, 40:13 and 45:13 showed the greatest growth, with average daily weight gain and specific growth ranging from 1.55 to 1.65 g/d and from 0.94 to 1.00%/d, respectively, over 77 days. FCR remained between 2.2 to 2.3, which is considered above average for cultured giant freshwater prawns, and did not differ among the dietary groups.

Carcass composition. The carcass composition of freshwater prawn fed experimental diets is shown in table 3. The experimental diets produced no appreciable differences in the prawns' moisture content. A nonsignificant tendency for an increased percentage of body protein with an increased dietary protein level was observed. The highest percentage was observed for the diet with a P:L ratio of 45:8 (20.3%), followed by the diets with a P:L ratio of 40:8 (20.1%) and 35:8 (19.0%). Carcass composition differed significantly between diets with higher protein levels and those with higher lipid levels (p<0.05).

DISCUSSION

The water quality parameters were within the acceptable range for prawn species (8). Diets were formulated using highly digestible ingredients similar to those used in experimental diets designed for prawns and other decapod crustaceans (9). The prawn accepted and tolerated the experimental diets quite, well and a gross examination revealed no pathological symptoms or abnormalities of any kind. Survival greater than 80.0% is considered good in crustacean studies (2).

Although the reported growth rates of cultured freshwater prawns are highly variable (10,11), variation was low among our treatment groups. This low variation may be attributed to the maintenance of nutritional quality across diets. Freshwater prawns fed various isonitrogenous diets containing soybean meal and fish meal as protein sources did not exhibit significantly different weight gain compared to controls. Similar growth rates were found for M. rosenbergii fed either a commercial shrimp diet or a diet containing fish meal, shrimp meal, soybean meal, mustard oilcake, sesame meal and rice bran (12). At this stage postlarval M. rosenbergii exhibit protein sparing (9).

Similar FCR values (2.18-2.43) were reported by Benítez-Mandujano and Ponce-Palafox (2). FCR is a measure of the proper consumption of feed by prawn since the rate of food consumption increases as the prawn grows until a certain age (12). In M. rosenbergii, Hossain et al (12) reported an FCR of 10-18:1 FCR for raw feeds, 2-3.5:1 for compounded diets, and 2.35 for a diet containing 37% protein. Higher FCR values of 3.7 (5 prawns/m2) to 5.6 (20 prawns/m²) were reported for M. rosenbergii cultured in concrete tanks and fed a diet containing 34% protein (13). However, feeding studies on M. carcinus have been conducted only at the level of postlarvae (14) and juveniles (2); adults and broodstock have not been studied in this regard.

Manush et al (13) fed juvenile Australian freshwater crayfish diets containing crude protein levels of 15%, 20%, 25% and 30% and found that carcass crude protein levels varied with respect to the dietary protein level. A linear relationship has also been demonstrated between dietary protein and fresh protein (15). We observed a similar relationship in M. carcinus adults: carcass crude protein levels were significantly higher in prawns fed high protein diets.

Diets with P:L ratios of 35:13, 40:13 and 45:13 containing soybean and fish meal as major protein sources resulted in significantly (p<0.05) higher carcass lipid content than those with 8% lipids. Similarly, Sambhu and Jayaprakas (16) saw no difference in the total length of Penaeus indicus fed different diets.

No significant difference in whole body moisture percentage was observed for different experimental treatments. Similar results were reported for M. rosenbergii (17). However, the proportion of total protein, amino acids, lipids, fatty acids, carbohydrates and RNA were higher in female M. rosenbergii than in the males (17). In contrast, the moisture and ash content were higher in males compared to females. Despite these differences, a trend was noted regarding effects produced by diets with increasing protein and lipid levels.

In conclusion, the data presented here suggest that the formulated experimental diets were efficiently utilized by M. carcinus broodstock to produce satisfactory growth and fresh quality. Significantly better growth (p<0.05) was observed in diets with 13% lipids compared with diets with 8% lipids. No significant differences were observed in the percentage of protein in muscle with an increasing dietary protein level. However, we found a tendency for improved nutritional quality of prawn in the diets containing 40 and 45% protein.

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