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Latin american journal of aquatic research

versión On-line ISSN 0718-560X

Lat. Am. J. Aquat. Res. vol.48 no.3 Valparaíso jul. 2020

http://dx.doi.org/10.3856/vol48-issue3-fulltext-2361 

Research Article

Production of Penaeus vannamei in low salinity, using diets formulated with different protein sources and percentages

Juan Carlos Gil-Núñez1 

Luis Rafael Martínez-Córdova2 

Rosalía Servín-Villegas3 

Francisco Javier Magallon-Barajas3 

Rafael Apolinar Bórquez-López4 

Jose Reyes Gonzalez-Galaviz5 

Ramón Casillas-Hernández4 

1Departamento de Biotecnología y Ciencias Alimentarias del Instituto Tecnológico de Sonora, Obregón Sonora, México

2Departamento de Investigaciones Científicas y Tecnológicas de la Universidad de Sonora, Hermosillo Sonora, México

3Centro de Investigaciones Biológicas del Noroeste, S.C., Instituto Politécnico Nacional La Paz, México

4Departamento de Ciencias Agropecuarias y Veterinarias del Instituto Tecnológico de Sonora, Obregón Sonora, México

5CONACYT - Instituto Tecnológico de Sonora, Obregón, Sonora, México

ABSTRACT

The present study was focused on assessing the effect of diets formulated with different sources and levels of protein on the production response of white leg shrimp Penaeus vannamei farmed at low salinity (3 g L-1). The protein sources were: soy meal (SM) and fish meal (FM), included at three levels: low (22-25%), medium (32-35%), and high (41-45%). A bioassay of 49 days was done in experimental tanks of 100 L (three tanks per treatment). Juvenile P. vannamei having a mean weight of 1.41 ± 0.30 g were stocked at a density of 100 ind m-3. Shrimp fed diets formulated with FM recorded significantly higher weight gain, specific growth rate (SGR), and protein assimilation efficiency rate (PER). Additionally, it showed a higher concentration of essential amino acids like methionine and threonine, and higher ash, calcium, iodine, phosphorous, and sodium content, which could favor the growth and survival of shrimp. Regression analysis showed that the optimum protein levels for diets formulated with SM and FM were 34.8 and 29.3%, respectively. These findings may help shrimp farmers to implement better feeding strategies for P. vannamei farmed at low salinity and on the use of alternative ingredients to substitute fish meal in the formulated feed.

Keywords: Penaeus vannamei; low salinity; soybean meal; replacement; diet; aquaculture

INTRODUCTION

Farming of white leg shrimp Penaeus vannamei at low salinity is a practice becoming popular in diverse regions of the world. The species ability to thrive in a salinity range from 0.5 to 45 g L-1, in waters with an adequate ionic balance, make it a viable alternative for culture in diverse aquatic environments (González-Félix et al., 2017), since it has been farmed in waters from wells as well as in salinized land unable for agriculture (Páez-Osuna & Valencia-Castañeda, 2013; Jarwar, 2015). Moreover, due to the negative effect that marine aquaculture has had as a result of various viral diseases, the inland farming of marine organisms has become a viable alternative (Fierro et al., 2018). However, the culture at low salinities faces some challenges, some of them related to nutrition and environmental sustainability (Chen et al., 2015).

The main aquafeeds protein ingredient is fish meal (FM), mainly because of its high digestibility, palatability, and balanced amino acid profile (NRC, 2011; Bauer et al., 2012; Huang et al., 2018). However, the increasing price and decreasing FM availability are two important problems for its use (Katya et al., 2016; Ayisi et al., 2017). Many different studies have been conducted to substitute FM in aquafeeds using some other protein sources such as fly meal, pea paste, cotton seeds, and poultry subproducts (Lim, 1996, 1997; Liu et al., 2012; Luo et al., 2012; Cabanillas-Beltrán et al., 2013; Carvalho et al., 2016; Cummins et al., 2017; Panini et al., 2017a,b). Soy meal (SM) has shown to be a good substitute for FM in diets for P. vannamei due to its high content of crude protein and good amino acid profile, as well as its low cost as compared to FM (Jatobá et al., 2017). There are many studies on the replacement of FM by SM in shrimp P. vannamei both in marine and low salinity environments, reporting the performance, protein efficiency ratio, daily feeding intake and mineral supplements (Xie et al., 2016; Huang et al., 2017; Jatobá et al., 2017; Moreno-Arias et al., 2018). However, the effect of the protein level of different sources has not been sufficiently explored in the culture at low salinity. For that reason, this study was focused on evaluating some sources with varying levels of protein on the productive performance of P. vannamei farmed at low salinities and found the optimal level for that condition.

MATERIALS AND METHODS

Diets preparation and chemical analysis

After analyzing the proximate chemical composition of the four meals (PIASA; La Paz, BCS, México) used as ingredients (fish meal: FM, soy meal: SM, soy protein concentrate: SPC, and wheat flour; WF), six isocaloric and isolipidic diets were prepared (Table 1). The formulation was done by using algorisms developed by Calderón (2007). Fish meal and SM were used as the main protein sources, and were included at three levels in the respective diets: low (L, 22-25%), medium (M, 32-35%) and high (H, 41-45%), resulting in the six experimental diets: FML, FMM, FMH, SML, SMM, SMH. In the six diets, fish oil was used as a lipid source. Diets based on animal protein were prepared with a mix of 36.4% FM, 36.4% SM, and 27.1% WM. Diets based on vegetal protein, were prepared with 45.0% soy protein concentrate, 30.0% SM, 20.0% WM and 2.4 to 4.4% FM as attractant (Table 2). The analyzes of amino acid and elemental components were done by HPLC accordingly to the method suggested by Vázquez-Ortiz et al. (1995).

Table 1 Results of bromatological analysis of each of the flours used in the preparation of experimental diets. 

Analysis Fish meal Soybean meal Soy protein concentrate Wheat flour
Moisture (%) 6.59 8.87 8.27 10.45
Crude protein (%) 72.95 50.95 64.70 13.38
Crude fat (%) 6.38 1.17 1.13 0.40
Ash (%) 16.98 7.16 3.54 0.80
Crude fibre (%) 0.13 2.80 4.33 0.30
Nitrogen-free extract (%) 3.56 38.05 26.30 85.12

Table 2 Formulation of the six experimental diets for Penaeus vannamei, based in vegetal and animal protein (g kg-1 diet). 

Treatment
SML SMM SMH FML FMM FMH
Fish meala 24.83 34.77 44.70 186.39 247.56 325.55
Soy protein concentrateb 223.50 312.92 402.36 0.00 0.00 0.00
Soybean mealc 149.00 208.62 268.24 186.39 247.56 325.55
Wheat flourd 99.33 139.08 178.83 138.86 184.43 242.53
Corn starche 371.19 190.08 8.95 356.19 168.96 0.00
Fish oilf 28.72 26.22 23.72 19.39 64.23 37.30
Soy lecithing 36.20 36.20 36.21 35.21 33.40 34.17
Mineral premixh 9.24 9.25 9.25 8.99 8.53 8.72
Vitamin premixi 9.24 9.25 9.25 8.99 8.53 8.72
Alginic acidj 18.49 18.49 18.49 17.98 17.06 17.45
Ashk 18.88 9.44 0.00 36.89 17.49 0.00
Cellulosel 11.34 5.67 0.00 4.70 2.23 0.00
Antioxidantm 0.01 0.01 0.01 0.01 0.01 0.01

SM: soy meal, FM: fish meal. SML: diet with 25% protein; SMM: diet with 35% protein; SMH: diet with 45% protein (based on mixture of vegetal proteins); FML: diet with 22% protein; FMM: diet with 32% protein; FMH: diet with 41% protein (based on mixture of vegetal and animal protein).

a)Whole sardine meal (72.95% crude protein, 6.38% lipid)*,

b)soy protein concentrate (SPC) (64.70% crude protein, 1.13% lipid)*,

c)soybean meal (50.95% crude protein, 1.17% lipid)*,

d)wheat flour (13.38% crude protein, 0.4% lipid)*,

e)corn starch (0.3% crude protein, 0.1% lipid), Maizena®,

f)fish oil*,

g)soybean lecithin*,

h)mineral premix*,

i)vitamin premix*,

j)alginic acid**,

k)ash**,

l)cellulose,

m)antioxidant.

*PIASA (La Paz, BCS, México), **Sigma-Aldrich Corp. 180947A2158 (St. Louis, MO, USA).

Obtaining and acclimation of experimental organisms

Shrimp postlarvae of Penaeus vannamei were obtained from Larvas Génesis S.A de C.V (Sonora, México). They were acclimated in plastic tanks under controlled conditions of temperature (28 ± 0.5°C), salinity (35) and dissolved oxygen (DO) (≥4 mg L-1), feeding them three times a day (08:00, 13:00 and 18:00 h), at satiations with a commercial feed (35% CP, crude proteins; 7% lipids). Feces and unconsumed feed were discarded by siphoning. Ten percent of the water was exchanged every 24 h. When shrimp reached 1.0-1.5 g bodyweight, the acclimation to the salinity process (from 35 to 3) was initiated, according to suggested by Van Wyk (1999).

Experimental design

A bioassay was conducted over 49 days to evaluate the experimental diets. A completely randomized experimental design with three replicate per treatment was performed. The experimental units consisted of 21 tanks of 200 L, three for each of the six diets, and three for the control. Each unit was stocked with 10 juveniles (100 ind m-3; 1.41 ± 0.30 g) which were maintained under relatively controlled conditions (temperature: 28 ± 0.5°C; pH: 8.3-8.4; DO: 6.40 ± 0.72 mg L-1; salinity: 3; photoperiod: 12:12 h).

Three times during the trial (days 1, 28 and 49), the concentrations of K+, Mg++, Ca++, Na+ and Cl, were measured by spectrophotometry (Spectroquant 300 Merck) with precisions around, 2.6, 1.6, 1.9, 2.4, and 2.1%, respectively. A water exchange of around 10% d-1 was applied. Shrimp were fed at satiation three times a day (08:00, 13:00, and 18:00 h), initiating with 10% of total shrimp biomass, adjusting it weekly. Unconsumed feed was removed and stored at 20°C. At the end of the trial, the production responses of shrimp: final weight (FW), % of weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), and survival (S) were estimated, accordingly to Peña-Rodríguez et al. (2017):

  • FW = Σ final individual weight / final number of shrimps

  • WG = 100 × (final weight - initial weight) / initial weight

  • SGR (% d-1) = 100 × (ln final weight - ln initial weight / days of culture)

  • FCR = consumed feed / (final weight - initial weight)

  • PER = (final weight - initial weight)/(consumed feed × protein concentration)

  • S = (number of harvested shrimp/number of stocked shrimp) × 100

Statistical analysis

Production parameters were analyzed by a two-way analysis of variance (after homoscedasticity and normality test) set to a confidence level of P < 0.05. The analysis was performed in the software Statgraphics XVI.

The optimal requirements of protein were estimated for the maximum WG by using the software MATLAB with the curve adjustment tools (Mathworks, 2012), using as independent variables, the three levels of each protein source. The selection criteria for curve adjusting were based on the determination coefficient (R2). From the second order-polynomial regression, the optimal level supporting the response of maximum WG was calculated (Li et al., 2016; Bórquez-Lopez et al., 2018).

RESULTS

Effect of a fish meal replacement on the proximate chemical composition, amino acid profile and elemental components of the diets

The proximate chemical composition and amino acid profile of diets are shown in Table 3. Ash content was higher in diets based on FM. The content of nitrogen-free extract (NFE) decreased as the percentage of protein supplemented increased, independently of the source of protein used. The energy content was similar among diets. Methionine and threonine content was a little lower in diets based on vegetal protein. Some elemental components such as Ca, I, P and Na, were found at higher proportion in diets based on FM.

Table 3 Proximate composition (g kg-1 fed), amino acid profile (% / %CP), and elementals compounds (ppm) of the six experimental diets for low salinity shrimp Penaeus vannamei elaborated with a different protein source (vegetal and animal). 

SML SMM SMH FML FMM FMH
Proximate composition (g kg-1 ms, except moisture)
Moisture 46.0 ± 2.2 12.2 ± 0.8 18.8 ± 0.3 47.6 ± 1.6 28.5 ± 0.5 39.8 ± 0.3
Crude protein 256.7 ± 0.3 356.3 ± 0.7 444.0 ± 2.0 227.3 ± 1.1 321.2 ± 1.2 405.2 ± 2.5
Crude fat 63.8 ± 1.0 66.5 ± 0.0 65.3 ± 0.6 58.0 ± 0.9 58.4 ± 0.5 58.6 ± 1.9
Crude fiber 12.6 ± 0.6 11.7 ± 0.6 13.3 ± 0.6 2.3 ± 0.6 2.3 ± 0.6 7.0 ± 1.0
Ash 55.3 ± 0.4 55.9 ± 0.3 56.1 ± 0.3 103.8 ± 0.4 108.6 ± 0.3 115.1 ± 0.3
NFE 611.6 509.6 421.3 608.6 509.5 414.1
Gross energy (kcal) 4.48 ± 0.002 4.64 ± 0.004 4.79 ± 0.001 4.20 ± 0.006 4.33 ± 0.002 4.41 ± 0.002
Amino acid profile (% / %CP)
Essential amino acid
Arginine 3.50 3.56 3.40 3.00 3.37 3.26
Phenylalanine 5.75 5.41 5.06 5.22 4.83 4.86
Histidine 5.20 5.55 7.18 5.68 6.89 7.64
Isoleucine 3.54 3.86 3.34 3.50 3.02 3.09
Leucine 5.94 7.04 6.09 5.78 5.33 5.15
Lysine 0.61 1.06 1.26 1.13 1.45 0.85
Methionine 2.70 2.07 1.81 2.84 2.54 2.17
Threonine 9.06 14.07 16.32 16.61 20.85 16.64
Valine 4.07 4.26 4.10 4.71 4.01 4.34
Nonessential amino acid
Alanine 2.48 3.60 3.54 3.69 4.38 3.87
Aspartic acid 5.45 5.17 5.94 4.89 6.23 5.99
Glutamic acid 18.42 15.56 17.44 13.68 16.41 15.21
Glycine 3.42 3.89 4.06 2.80 3.59 3.30
Serine 2.60 2.90 3.15 2.17 2.36 2.49
Tryptophan 11.90 5.56 6.33 9.48 7.49 8.25
Elementals compounds
Ca 6283.6 6400.1 7412.2 14337.0 17700.5 26739.3
Cu 50.8 50.6 53.8 45.6 53.0 59.8
Fe 418.9 413.5 597.5 613.8 417.5 970.3
K 4143.3 5922.3 6453.1 3886.0 6289.4 6328.6
Mg 1227.5 1444.7 1862.5 1375.9 1763.4 2696.4
Mn 22.6 26.9 35.0 23.1 26.4 41.0
Na 3281.8 3077.2 2822.8 3717.8 4792.5 4310.3
P 4876.1 5863.3 7014.5 8312.6 10406.4 15861.7
S 807.7 929.1 1185.1 725.5 891.0 1336.5
Si 37.8 20.9 19.0 33.8 31.9 26.7
Zn 129.8 120.6 132.0 138.2 139.8 183.3
N 32550.0 94150.0 57050.0 35350.0 43750.0 51450.0

SM: soy meal, FM: fish meal. SML: diet with 25% protein; SMM: diet with 35% protein; SMH: diet with 45% protein (based on mixture of vegetal proteins); FML: diet with 22% protein; FMM: diet with 32% protein; FMH: diet with 41% protein (based on mixture of vegetal and animal protein).

Water quality parameters

Table 4 shows the water quality parameters, including the concentration of specific ions. Mean temperature was 28.2 ± 0.59°C, mean DO 6.4 ± 0.72 mg L-1, mean pH 8.37 ± 0.06 and mean salinity 3.19 ± 0.15. The Mg++, Na+, and Cl concentrations remained under the optimal values required. The Na+/K+ rate ranged from 21:1 to 23:1 in the treatments.

Table 4 Water quality results (mean ± standard deviation) of low salinity shrimp (Penaeus vannamei) cultured for 49 days fed six experimental diets and one commercial diet (n = 3). 

Water quality parameter Treatment
SMl SMm SMH FMl FMm FMH DC *Optimal value
Temperature (°C) 28.2 ± 0.58 28.3 ± 0.66 28.7 ± 0.58 28.2 ± 0.59 28.2 ± 0.57 28.2 ± 0.57 28.2 ± 0.59 24-32
Dissolved oxygen (mg L-1) 6.7 ±0.77 6.4 ± 0.74 6.3 ± 0.71 6.4 ± 0.72 6.4 ± 0.67 6.4 ± 0.75 6.4 ± 0.68 ≥4.0
pH 8.4 ± 0.06 8.4 ± 0.06 8.4 ± 0.05 8.4 ± 0.06 8.4 ± 0.08 8.4 ± 0.07 8.4 ± 0.07 7-9
Salinity 3.2 ±0.19 3.2 ± 0.15 3.2 ± 0.20 3.2 ± 0.09 3.2 ± 0.11 3.2 ± 0.15 3.2 ± 0.15 0.5 - 40.0
Potassium (mg L-1) 38.3 ±5.36 37.3 ± 4.44 39.9 ± 4.53 37.8 ± 5.15 38.3 ± 3.92 38.7 ± 3.01 35.9 ± 5.71 33.9
Magnesium (mg L-1) 66.9 ±15.8 52.6 ± 17.7 67.1 ± 17.4 62.3 ± 12.0 64.1 ± 12.9 65.2 ± 14.7 51.0 ± 11.8 109.5
Calcium (mg L-1) 53.9 ±12.9 49.5 ± 8.4 58.2 ±13.0 52.8 ± 12.4 55.6 ± 14.5 53.6 ± 11.2 45.7 ± 9.3 35.1
Sodium (mg L-1) 868.9 ± 245.6 771.1 ± 196.5 906.7 ± 201.1 818.9 ± 210.3 888.9 ± 148.8 873.3 ± 176.1 644.4 ± 316.7 919.8
Chloride (mg L-1) 1530.0 ±228.6 1468.9 ± 264.8 1657.8 ± 255.5 1576.7 ± 349.6 1674.4 ± 247.6 1588.9 ± 184.8 1422.2 ± 431.5 1650.9
Relation Na+/K+ 23:1 21:1 23.1 23:1 23:1 23:1 18:1 23:1

SM: soy meal, FM: fish meal. SML: diet with 25% protein; SMM: diet with 35% protein; SMH: diet with 45% protein (based on mixture of vegetal proteins); FML: diet with 22% protein; FMM: diet with 32% protein; FMH: diet with 41% protein (based on mixture of vegetal and animal protein).

*(Paez-Osuna & Valencia, 2013; Hongyu et al, 2014).

Effect of experimental diets, on the production response and feed use efficiency

Table 5 presents the production response parameters, and the feed use efficiency of shrimp fed the experimental diets and the control. The weight gain rate ranged from 219 to 389%, the SGR from 1.01 to 1.41%, the survival from 60.0 to 93.3%, the FCR from 1.64 to 2.15. The PER varied from 0.92 to 2.83. The WG showed significant differences among diets FML and SML (P < 0.05).

Table 5 Productive parameters of juvenile white shrimp Penaeus vannamei (initial weight 1.41 ± 0.30 g) to the experimental treatments after seven weeks feeding trial. 

Source protein Level protein FW WG SGR FCR PER S
Vegetal Low (SML) 4.4a 219.4a 1.0a 1.7a 1.7ab 56.6ab
Medium (SMM) 5.4abc 288.3abc 1.2ab 1.6a 1.4ab 93.3c
High (SMH) 4.9ab 248.3ab 1.1ab 2.0a 0.9a 50.0a
Animal Low (FML) 6.2bc 336.7bc 1.3ab 1.8a 2.3ab 90.0bc
Medium (FMM) 6.6c 389.8c 1.4b 1.8a 2.8b 90.0bc
High (FMH) 6.2bc 340.5bc 1.3ab 2.2a 1.9ab 73.3abc
Control Medium (DC) 4.9ab 237.8ab 1.1ab 1.6a 1.6ab 90.0bc
Effects P-value
A 0.00 0.00 0.00 0.38 0.01 0.68
B 0.20 0.28 0.26 0.08 0.22 0.39
AB 0.75 0.94 0.87 0.83 0.57 0.08

Lowercase letters in the same column indicate homogeneous subsets as determined by Tukey's test (α = 0.05). FW: final weight, WG: weight gain (%), SGR: specific growth rate, FCR: feed conversion ratio, PER: protein efficiency ratio, S: survival. SM: soy meal, FM: fish meal. SML: diet with 25% protein; SMM: diet with 35% protein; SMH: diet with 45% protein (based on mixture of vegetal proteins); FML: diet with 22% protein; FMM: diet with 32% protein; FMH: diet with 41% protein (based on mixture of vegetal and animal protein); DC: diet control (commercial feed: 35% crude proteins; 7% lipids). A: source protein, B: level protein, AB: source protein and level protein.

Effect of experimental diets on the optimal protein level and maximum weight gain

Table 6 shows the optimal protein level for the two sources of protein used. For diets based on FM, the optimal level was 29.3%, while for those based on SM, it was 34.8%.

Table 6 Optimal dietary protein level for the different protein sources; polynomial equations obtained from MATLAB curve fitting toolbox. 

Source protein Level protein Weight gain (%) *Equation Coefficient of determination (R2) Optimal dietary protein level (%)
Vegetal Low 219.4 ± 78.1 Y = -1.3661x2+95.112x–1400.9 1.0 34.8
Medium 288.3 ± 31.7
High 248.3 ± 88.9
Animal Low 336.7 ± 44.6 Y = -1.0206x2+59.814x–547.25 1.0 29.3
Medium 389.8 ± 20.6
High 340.5 ± 86.5

*Equation; vegetal: relationship between body weight gain (WG) and vegetal dietary protein levels; animal: relationship between body weight gain (WG) and animal dietary protein levels.

DISCUSSION

As a relatively recent activity in México, farming marine shrimp at low salinity requires yet much investigation, mainly that related to the effects of the ionic composition of the water on the development and productive response of the organisms (Saoud et al., 2003; Roy et al., 2010; Perez-Velazquez et al., 2012; Valenzuela-Madrigal et al., 2017). The survival around 79% obtained in the present study was similar to the reported by other authors, such as Chen et al. (2015) and Gao et al. (2016) when farmed P. vannamei at salinities from 2 to 3. The low survivals around 50-60% recorded in some units (SML and SMH) are probably associated with problems of water quality, nutrition, or a combination of both. A low supply of dietary protein could be conduct to poor nutrition and low resistance of the organisms to stressing factors as a drastic decrease in salinity. On the other hand, an excess of protein supply is responsible for high nitrogen metabolites such as ammonia (mainly as NH3), which provoke stress, low feed consumption decrease in oxygen transport by hemolymph, low growth, and eventually, mortalities.

An adequate ionic balance in the water column, mainly of Ca+2, Mg+2, and K+, favored the physiologic response of the shrimp and improves growth, molt process, efficiency on the feed utilization, nutrients assimilation, hemolymph coagulation, nervous transmission, muscular contraction, osmoregulation, and as co-factor in diverse enzymatic processes (Davis et al., 2004; Cheng et al., 2006; Zhu et al., 2006). Páez-Osuna & Valencia-Castañeda (2013), suggest that the concentration of the major ions in the cultivation water must be equivalent to that contained in the seawater, which can be calculated using the equation:

CEx=(S)(R×)

where CEx is the equivalent concentration of seawater, S is the salinity of the pond water, and Rx is the ratio of the seawater concentration to the normal seawater salinity.

The Rx values to estimate the acceptable concentrations of each ion in shrimp culture in low salinity water are 11.3 for potassium (K+), 306.6 for sodium (Na+), 11.7 for calcium (Ca+2), 36.5 for magnesium (Mg+2), 77.1 for sulfates (SO4-2) and 550.3 for chlorides (Cl). In the present study, the K+ and Ca+2 values were over the recommended levels, while Mg+2, Na+, and Cl were under those levels (Millero, 2006).

The low concentration of Cl and Na+, which should have been ≥1650.9 and 919.8 mg L-1 respectively, to have them in balance, probably affected the hyper-osmoregulation, since these ions are the main responsible of this metabolic process, particularly in shrimp farmed at low salinity (Davis et al., 2004; Huong et al., 2010). Otherwise, the Na+/K+ rate is crucial for the osmoregulation process. Rates ranged from 21:1 to 23:1 during the trial, similar to what Hongyu et al. (2014) reported. They investigated the effect of different Na+/K+ rates in Penaeus vannamei cultures at 4, obtaining the best results at a rate of 23:1. They suggest that this rate is important for a good activity of Na+/K+-ATPase, responsible for the ionic interchange in the osmoregulation process.

A good protein source for animal nutrition purposes is that with a balanced content of amino acids. The recommended percentages for P. vannamei culture are: arginine (5.8%), methionine (2.4%), cysteine (3.6%), threonine (3.6%), valine (4.0%), isoleucine (3.4%), leucine (5.4%), lysine (5.3%), histidine (2.1%), phenylalanine (4.0%), phenylalanine + tyrosine (7.1%) and tryptophan (0.8%) (Puello-Cruz, 2013). Some amino acids are essential for diverse shrimp metabolic processes. These include the maintenance of osmolality, osmoregulation, and influence growth and survival (Perez-Velazquez et al., 2009). Table 3 shows the amino acid profile of experimental diets evaluates in the present study. Lysine, threonine, and alanine recorded low concentration, particularly in the diet SML, in which low weight gain and survival of shrimp was observed. Threonine is considered important for shrimp immune systems and influence their growth and feed assimilation efficiency (Zhou et al., 2013). In the present study, the content of threonine in the experimental diets ranged from 9.06 to 20.85%, within the levels required by the species which at low salinity is around 3.78% (Huai et al., 2009; Zhou et al., 2013). The levels of methionine were also low in the diets, mainly in SMH (the diet with the higher FM replacement). The values were similar to the reported by Bauer et al. (2012), who found that methionine and threonine decreased as the replacement of FM increased. Methionine is considered an essential amino acid for shrimp, recommended at levels from 1.9 to 2.9 to cover the requirements of P. vannamei (Lin et al., 2015; Façanha et al., 2016). In this trial, the deficiency in methionine coincided with a low survival of shrimp.

The results of the present study demonstrated that both source and level of protein had a significant influence on the production parameters of shrimp farmed at low salinity (Table 5). Diets containing more FM produced the best growth, survival, and protein efficiency, which can be attributed to the desirable characteristics for the feed shrimp above, which are high digestibility and attractiveness, as well as a balanced amino acid profile (Huang et al., 2018).

The optimal protein level for diets based on animal sources was 29.3%, while for those based on vegetal sources, it was 34.8% (Table 6). The difference could be attributed to the amino acid profile, digestibility, and in general, the nutritional composition (Jannathulla et al., 2017; Huang et al., 2018). Additionally, diets based on vegetal sources typically contain anti-nutritional components such as lectin and folic acid (et al., 2013), which are trypsin inhibitors (Zhou & Davis, 2015), or saponins (Xie et al., 2016). Which form mineral complexes affecting the nutrient absorption by shrimp (Xie et al., 2016; Kokou & Fountoulaki, 2018). The optimal levels of protein recommended for white shrimp farming at low salinity ranged from 30 to 36% (Kureshy & Allen-Davis, 2002; Hu et al., 2008; Xu & Pan, 2014). Some other authors (Liu et al., 2012; Gao et al., 2016; Huang et al., 2017) reported optimal values from 26 to 40%. The levels obtained in the present study are within the range indicated by the authors mentioned above. Some other factors influencing the optimal protein level for shrimp include size, environmental conditions, culture system, natural productivity, non-protein energy, and alternative ingredients (Martínez-Córdova et al., 2013; Shahkar et al., 2014). The PER of the experimental diets evaluated in this study shows that the values decreased as the protein level increased, agreeing with that reported in other studies, and it is attributed to the use of protein excess as energy source instead of mass formation (Shahkar et al., 2014). An important issue to consider is the carbohydrate content expressed as nitrogen free extract in the diets (NFE) (Table 3). It is interesting to observe the inverse correlation between protein level and NFE content, independently of the protein source. The NFE levels varied from 42.1 to 61.1% in diets SM, and from 41.4 to 60.9% in FM. It is well known that when P. vannamei is farmed at low salinity, the energetic cost for metabolic processes as osmoregulation, increases significantly (Pillai & Diwan, 2002).

This requirement could be cover by carbohydrates instead protein, permitting it to be used for tissue formation (Perez-Velazquez et al., 2009). Wang et al. (2004) reported a higher SGR for P. vannamei when carbohydrate supply was around 16%, in our experimental diets carbohydrate content was in the levels required by the species, and favored the idea that NFE values could be in part responsible for the results of the higher protein efficiency ratio when NFE/Protein ratio increase. However, it is important to consider this energetic source in further assays of sources and levels of protein in shrimp, mainly when a source of protein or carbohydrate would be substituted in order to avoid a decompensation in dietary energy.

It is plausible to conclude that for P. vannamei low salinity cultures, it is necessary an adequate ionic water balance. Where ions that are deficient (according to the shrimp requirement) must be added by using some products already recommended for aquaculture, as potassium sulfate (K2SO4), calcium chloride (CaCl2), magnesium sulfate and potassium (MgSO4-K2SO4), among others. It is possible to use diets based on vegetal or animal sources. Still, the level of protein must be different: 34.8 and 32.1%, respectively, because fishmeal is a better source of minerals, trace elements, amino acid profile, digestibility, attractiveness, among other characteristics desired in shrimp feed.

ACKNOWLEDGMENTS

J.C. Gil-Nuñez is grateful for financial support of Consejo Nacional de Ciencia y Tecnología with PhD scholarship. This study was supported by Instituto Tecnológico de Sonora Project PROFAPI_2020_0093 and PROFAPI_2020_0119. The authors also thank the Consejo Nacional de Ciencia y Tecnologıa for supporting project No. 1037 of Cátedras CONACYT.

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Received: June 06, 2019; Accepted: January 31, 2020

Corresponding author: Ramón Casillas-Hernández (ramon.casillas@itson.edu.mx)

Corresponding editor: Fernando Vega

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