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Introduction
Microalgae contain high-value nutrients such as carotenoids, vitamins, and essential fatty acids (Hamed 2016). Consequently, they are a primary food source for many marine organisms during their early life stages, including bivalves, fish, and shrimp, as well as zooplankton such as Artemia, cladocerans, and copepods (Martínez-Córdova et al. 2014).
Carotenoids, which are vitamin A precursors, can scavenge reactive oxygen species, protecting cells from aggressive free radical damage and improving the immune system (De la Vega-Naranjo 2014, Ruiz-Soto 2017). Similarly, chlorophylls function as antioxidants by interrupting the peroxidation chain reaction (Rigane et al. 2013). Polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA, 20:5 n-3), docosahexaenoic acid (DHA, 22:6 n-3), and arachidonic acid (AA, 20:4 n-6; Ramírez-Mérida et al. 2015), are essential for organisms. These compounds play important functions as precursors of eicosanoids and hormones and improve the immune system (Vizcaíno-Ochoa et al. 2010).
The diatoms Thalassiosira weissflogii and Chaetoceros muelleri mainly produce the carotenoids fucoxanthin, diadinoxanthin, diatoxanthin, and β-carotene (Marella and Tiwari 2020). However, they can produce other carotenoids, including violaxanthin, zeaxanthin, and phaeophytin a, in minor quantities depending on light, nutrient, and temperature conditions (Long et al. 2018). Tetraselmis suecica is characterized by having trans-violaxanthin, antheraxanthin, astaxanthin, lutein, α-carotene, and β-carotene (Ahmed et al. 2014), whereas Nannochloropsis sp. mainly contains violaxanthin and vaucheriaxanthin, in addition to zeaxanthin, canthaxanthin, α-carotene, and β-carotene (Paliwal et al. 2016). The main fatty acids in Thalassiosira weissflogii are 16:1n, 16:0, 14:0, and EPA, while those in Chaetoceros muelleri are 16:1n, 16:0, 14:0, EPA, and AA (Aranda-Burgos et al. 2014, Marella and Tiwari 2020). The green microalgae Tetraselmis suecica mainly contains 16:0, 16:2, 16:3, and α-linolenic acid (18:3), whereas Nannochloropsis sp. mainly contains EPA and AA (Chaisutyakorn et al. 2018, Pugkaew et al. 2019).
Artemia is one of the most used live foods in aquaculture, although Artemia nauplii and juveniles are deficient in PUFAs and carotenoids. These deficiencies can be solved by enrichment or bioencapsulation techniques, which can deliver several compounds of nutritional interest to organisms cultured with live food, including Artemia (Tlusty et al. 2005). Employing Artemia juveniles or adults has certain advantages over using nauplii, as their nutritional value is higher than that of recently hatched or early-stage nauplii (Léger et al. 1986).
In late developmental stages, Artemia is used as live food for larger organisms, including the lobster Homarus americanus, shrimp Macrobrachium americanum, and octopus Octopus vulgaris (Méndez-Martínez et al. 2018). In addition, Artemia is used widely in the culturing protocols of ornamental fishes. For example, Azimirad et al. (2016) evaluated the effect of feeding angelfish (Pterophyllum scalare) adult Artemia without enrichment (control), adult Artemia enriched with lyophilised probiotic, adult Artemia enriched with a prebiotic, and adult Artemia enriched with a synbiotic and found better results in terms of the final weight, weight gain, and specific growth rate of juvenile angelfish fed with the symbiotic-enriched Artemia.
Among Artemia species, A. franciscana is the most widely used live food in marine hatcheries despite being deficient in carotenoids and PUFAs. Nonetheless, as microalgae constitute the primary food source for Artemia, the biochemical composition of hatchery diets can be modified by adjusting the diet of Artemia (Fábregas et al. 2001). For example, several studies have shown that PUFAs can be transferred from microalgae to Artemia nauplii through feeding, that is, from prey to predator (Bhuvaneshwari et al. 2018). Indeed, a short enrichment period of 6-8 h was observed to improve the nutritional quality of Artemia, increasing PUFA content to 56.50% when enriched with Nannochloropsis salina (Chakraborty et al. 2007). Additionally, mortality rates of Artemia decreased when fed a diet enriched with this microalga (Chakraborty et al. 2007).
Many studies have evaluated the enrichment of Artemia nauplii with microalgae. However, very few have focused on Artemia in late developmental stages (i.e., juveniles and adults). Therefore, this study aimed to characterize the proximal composition, concentration of chlorophyll a and b, and total carotenoid content of the most widely used microalgae in aquaculture, namely Thalassiosira weissflogii, Chaetoceros muelleri, Tetraselmis suecica, and Nannochloropsis sp., to evaluate the effects of these microalgae diets on the biochemical composition of A. franciscana juveniles.
Materials and methods
Microalgae cultures
Microalgae were cultivated in f culture media prepared with seawater at 35 psu (practical salinity units), filtered and disinfected with commercial sodium hypochlorite at 5% (Guillard and Ryther 1962). Air was supplied continuously by a 2.5-HP blower, and the cultures were illuminated with 6 white light fluorescent lamps (6,000-6,500 lux). Temperature was maintained at 25 ± 1 °C. Microalgae culturing was carried out following the successive transfer technique of Zazueta-Patrón (2016) using the strains Thalassiosira weissflogii (TH-W-1), Chaetoceros muelleri (CH-M-1), Tetraselmis suecica (TE-S-1), and Nannochloropsis sp. (NN-X-1). The initial density of each culture was 10,000 cell∙mL-1 (TH-W-1), 200,000 cell∙mL-1 (CH-M-1), 25,000 cell∙mL-1 (TE-S-1), and 300,000 cell∙mL-1 (NN-X-1). Cultures were maintained until the exponential phase. Cell density was determined by direct counts using a compound microscope and Neubauer chamber. Representative samples of each microalga were taken to analyze the proximal composition of proteins, carbohydrates, and lipids, as well as the concentration of chlorophyll a and b, and total carotenoid content. All samples were kept at -60 °C until analyzed.
Culture of juvenile Artemia franciscana
To obtain A. franciscana nauplii (Great Salt Lake Artemia, INVE Aquaculture, lot 7116496181), we followed the standard cyst hydration-decapsulation-incubation procedure described by Sorgeloos et al. (1986). Based on mitogenomic analyses, Sainz-Escudero et al. (2021) proposed the name Artemia monica Verrill, 1869 as the valid name of A. franciscana Kellogg, 1906 for the New World Lineage. Hydration was conducted in freshwater with constant aeration. For decapsulation, 5% commercial sodium hypochlorite was used, and the cysts were incubated for 24 h in seawater (35 psu and 28 °C) with aeration and constant lighting (2,000 lux). After hatching, A. franciscana organisms were transferred to a 14-L container with 2 Artemia∙mL-1 and cultured for 9 days. During this period, A. franciscana was fed daily with Chaetoceros muelleri according to the feeding rate reported by Millán-Almaraz et al. (2021). The seawater was exchanged (30%) each day. The bioencapsulation experiment commenced on day 9 of the culture. Artemia franciscana was cultured for 9 days, as this time is required for organisms to reach the juvenile stage (minimum length of 2.7 mm; Sorgeloos et al. 1986).
Nutrient bioencapsulation experiment in juvenile Artemia franciscana
The microalgae and A. franciscana cultures were synchronized so that A. franciscana juveniles were available by the time the microalgae reached the exponential phase. Thus, we were able to feed isolipidic diets to the juveniles. The isolipidic equivalence of the microalgae has been determined in previous unpublished studies (Table 1). For this purpose, the microalgae Chaetoceros muelleri was used as a reference, and the experimental conditions were based on the results of Millán-Almaraz et al. (2021), who observed that the highest ingestion rate of A. franciscana juveniles occurred when they were fed with a density of 900,000 cell∙mL-1 in the dark. Therefore, considering the lipid content of the microalgae Chaetoceros muelleri (12.84 pg of lipid∙cell-1) and the reported cell density, the isolipidic diet consisted of 11,556,000 pg of lipid∙mL-1. Thus, we needed 77,541 cell∙mL-1 of Thalassiosira weissflogii, 457,482 cell∙mL-1 of Tetraselmis suecica, and 4,736,065 cell∙mL-1 of Nannochloropsis sp. to reach this concentration (Table 1).
Table 1 Lipid concentration in pg∙cell-1 and equivalence in cell∙mL-1 of the microalgae Thalassiosira weissflogii (TH-W-1), Chaetoceros muelleri (CH-M-1), Tetraselmis suecica (TE-S-1), and Nannochloropsis sp. (NN-X-1).
| CH-M-1 | TH-W-1 | TE-S-1 | NN-X-1 | |
| Lipids in pg∙cell-1 | 12.84 | 149.03 | 25.26 | 2.44 |
| Equivalence in cell∙mL-1 | 900,000 | 77,541 | 457,482 | 4,736,065 |
It is important to mention that before the experiment, the intestines were confirmed to be empty by direct observation using an CH30 microscope. The experiment consisted of 4 treatments, each with one species of microalgae and 4 replicas, resulting in 16 containers with microalgae + Artemia. The control did not include microalgae. In total, there were 20 experimental units, each with a density of 0.5 Artemia∙mL-1. The experimental units consisted of plastic containers with transparent walls, each with a useful volume of 14 L. During the experiment, salinity (35 psu), temperature (25 °C), aeration, and darkness (containers protected from light with black curtains) were maintained constant. At the beginning (0 h) and end (6 h) of the experiment, samples of A. franciscana juveniles were taken to determine the proximal composition of proteins, carbohydrates, and lipids, as well as the concentration of chlorophyll a and b, and total carotenoid content.
Proximal analysis
The proximal composition of the microalgae and A. franciscana juveniles was determined based on the dry weight of proteins (Lowry et al. 1951), carbohydrates (extraction, Whyte 1987; quantification, Dubois et al. 1956) and lipids (extraction, Bligh and Dyer 1959; quantification, Pande et al. 1963). To obtain the samples, a known volume of A. franciscana culture was filtered through GF/C 25 mm filters Whatman. Then, the samples were placed in an oven at 45 °C to dry and stored at -60 °C until analyzed.
Proteins
The filters containing the samples were placed in centrifuge tubes, and 2 mL of 1 N NaOH was added to each. Afterward, the filters were macerated, and 3 mL of 1 N NaOH was added. Then, the tubes were covered with aluminum foil and placed in a water bath at 100 °C for 10 min. Subsequently, the samples were mixed and centrifuged at 3,220 × g for 15 min, and the supernatant was transferred to the test tubes. A double extraction was performed. Afterward, 1 mL of each sample was collected and placed in each test tube, and 5 mL of solution C was added. Solution C was a mixture of the following solutions: solution A (2% anhydrous sodium carbonate in 0.1 N NaOH), solution B1 (0.5% copper sulfate in distilled water), and solution B2 (1% sodium potassium tartrate in distilled water). After adding solution C, the test tubes were allowed to settle for 10 min. Then, 0.5 mL of solution D (mixture of Folin Ciocalteu and distilled water) was added to each tube and shaken vigorously until the mixture turned blue. After which, the test tubes were left to stand for 90 min in the dark. A 1-cm quartz cell was used to read the samples in a Hach DR5000 spectrophotometer at a wavelength of 750 nm.
Carbohydrates
The filters containing the samples were placed in centrifuge tubes, and 2 mL of 1 M H2SO4 was added to each tube. Afterward, the filters were macerated, and 2 mL of 1 M H2SO4 was added. The tubes were covered with aluminum foil and placed in a water bath at 100 °C for 60 min. Subsequently, the samples were mixed and centrifuged at 3,220 × g for 15 min.
After centrifugation, 1 mL of the supernatant from each tube was taken and placed in a test tube, and 1 mL of 5% phenol solution was added. After resting for 40 min, 5 mL of concentrated sulfuric acid was added slowly and mixed until the samples turned yellow. Finally, a 1-cm quartz cell was used to read the samples in the Hach DR5000 spectrophotometer at a wavelength of 485 nm.
Lipids
The filters containing the samples were placed in test tubes and positioned in an ice bath. Then, 0.5 mL of distilled water and 2 mL of methanol were added to each tube, and the contents were macerated. Subsequently, 2 mL of chloroform and 2 mL of methanol were added to each tube and centrifuged at 3,220 × g for 15 min. Then, a double extraction was conducted using 1 mL of methanol and 2 mL of chloroform. A total of 2 mL of distilled water was added to the supernatant obtained from the 2 extractions, and the tubes were shaken vigorously for biphase formation. The tubes with the supernatant were covered with aluminum foil and refrigerated for at least 24 h. After which, the upper layer was discarded, and the rest was left to dry in an oven at 45 °C.
A total of 3 mL of the 2% acid solution of potassium dichromate was added to the remaining concentrate, which was then covered with aluminum foil and placed in a water bath at 100 °C for 15 min. Subsequently, 4.5 mL of distilled water was added to each tube, mixed vigorously, and cooled to room temperature. Finally, a 1-cm quartz cell was used to read the samples in the Hach DR5000 spectrophotometer at a wavelength of 590 nm.
Chlorophyll and total carotenoid analysis
Microalgae and Artemia samples were ground in 100% acetone in an ice bath in the dark and left to stand for 24 h in a refrigerator at 4 °C. The supernatant was recovered by centrifugation at 3,220 × g for 15 min at 4 °C. A double extraction was then performed on the precipitate, and the resulting supernatants were mixed. Then, a 1-cm quartz cell was used to read the samples in the Hach DR5000 spectrophotometer at 662 nm (chlorophyll a), 645 nm (chlorophyll b), and 470 nm (total carotenoids). The concentrations of these pigments are presented in µg·mL-1 and were calculated according to the equations proposed by Lichtenthaler and Wellburn (1983):
where Chla is chlorophyll a in µg∙mL-1, Chlb is chlorophyll b in µg∙mL-1, TC is total carotenoids in µg∙mL-1, and A is absorbance.
Statistical analysis
Data of the proximal composition, concentration of chlorophyll a and b, and total carotenoid content of the microalgae and juvenile A. franciscana were evaluated by Lilliefors normality and Bartlett homoscedasticity tests (Zar 2010) to determine if parametric or non-parametric statistical tests were necessary. When the data met the assumptions of these tests, a one-way analysis of variance (ANOVA) was performed. Conversely, when the data did not meet these assumptions, a non-parametric Kruskal-Wallis test was conducted. When significant differences were found, a Student-Newman-Keuls (SNK) multiple comparison test was conducted for both parametric and non-parametric data. Data analyzed with non-parametric tests are marked in the tables with an asterisk (*). All statistical analyses were performed in SigmaStat v. 3.5 with a significance level of 5%.
Results
Proximal analysis of microalgae
The proximal analysis based on dry weight (DW) revealed that the protein content of TE-S-1 (426.28 mg∙g-1) was higher than that of TH-W-1 and CH-M-1 (P < 0.05; Table 2). The carbohydrate content of TE-S-1 (231.70 mg∙g-1) was higher than those of CH-M-1 and NN-X-1 (P < 0.05; Table 2). On the other hand, TE-S-1 showed the highest lipid content (154.43 mg∙g-1), which was only significantly higher than that of NN-X-1 (P < 0.05; Table 2).
Table 2 Proteins, carbohydrates, and lipids in mg∙g-1 of dry weight of the microalgae Thalassiosira weissflogii (TH-W-1), Chaetoceros muelleri (CH-M-1), Tetraselmis suecica (TE-S-1), and Nannochloropsis sp. (NN-X-1) during their exponential phase. Results are mean values ± standard error (n = 4).
| Determination | Concentrations in mg∙g-1 | |||
| TH-W-1 | CH-M-1 | TE-S-1 | NN-X-1 | |
| Proteins | 244.70 ± 22.17a | 286.05 ± 19.19ab | 426.28 ± 57.26c | 389.75 ± 24.13bc |
| Carbohydrates | 185.57 ± 10.89b | 77.42 ± 7.37a | 231.70 ± 30.00b | 116.50 ± 8.32a |
| Lipids | 117.99 ± 2.89ab | 123.96 ± 5.67ab | 154.43 ± 19.64b | 105.89 ± 6.25a |
Equal letters indicate that there are no significant differences between species (P > 0.05).
Chlorophyll a, chlorophyll b, and total carotenoids in microalgae
The chlorophyll a content of TE-S-1 was 12.59 pg Chla·ng-1 DW, the highest value for all microalgae (P < 0.05; Table 3). The chlorophyll b content of TE-S-1 was 3.64 pg Chlb·ng-1 DW and was not significantly different from that of NN-X-1 (2.45 pg Chlb·ng-1 DW; P > 0.05; Table 3). The total carotenoid content of CH-M-1 (2.98 pg TC·ng-1 DW) and TE-S-1 (3.72 pg TC·ng-1 DW) reflected the highest concentrations of total carotenoids and were not significantly different (P < 0.05; Table 3).
Table 3 Chlorophyll a (Chla), chlorophyll b (Chlb), and total carotenoids (TC) shown as pg·ng-1 of dry weight (DW) of the microalgae Thalassiosira weissflogii (TH-W-1), Chaetoceros muelleri (CH-M-1), Tetraselmis suecica (TE-S-1), and Nannochloropsis sp. (NN-X-1) cultured during their exponential phase. Results are mean values ± standard error (n = 4).
| Unit | TH-W-1 | CH-M-1 | TE-S-1 | NN-X-1 |
| Chlorophyll a | ||||
| pg Chla·ng-1 DW | 8.93 ± 0.41a | 7.50 ± 0.54a | 12.59 ± 1.42b | 7.60 ± 0.72a |
| Chlorophyll b | ||||
| *pg Chlb·ng-1 DW | 1.02 ± 0.08b | 0.76 ± 0.05a | 3.64 ± 0.46c | 2.45 ± 0.26c |
| Total carotenoids | ||||
| pg TC·ng-1 DW | 1.96 ± 0.12a | 2.98 ± 0.18b | 3.72 ± 0.40b | 1.61 ± 0.14a |
Equal letters indicate that there are no significant differences between the species per unit of measure (P > 0.05). * Non-parametric test.
Proteins, lipids, and carbohydrate content in juvenile Artemia franciscana
After 6 h, all juveniles fed with different microalgae species exhibited higher concentrations and percentages of proteins, lipids, and carbohydrates compared to those of the initial and control values (Table 4). Organisms fed with TE-S-1 showed the highest content of proteins (41.12 µg∙org-1), lipids (11.90 µg∙org-1), and carbohydrates (8.70 µg∙org-1), which were significantly higher (P < 0.05) than those of the other treatments. On the other hand, the TH-W-1 and TE-S-1 treatments showed higher percentages of proteins (53.36% and 54.11%) and carbohydrates (11.32% and 11.45%), while TE-S-1 exhibited a higher percentage of lipids (15.66%; P < 0.05).
Table 4 Proteins, lipids, and carbohydrates (µg∙org-1 and percentages) based on the dry weight of Artemia franciscana juveniles at the beginning (0 h) and after (6 h) feeding them with Thalassiosira weissflogii (TH-W-1), Chaetoceros muelleri (CH-M-1), Tetraselmis suecica (TE-S-1), and Nannochloropsis sp. (NN-X-1). Results are mean values ± standard error (n = 4).
| Determination | Initial | Control | TH-W-1 | CH-M-1 | TE-S-1 | NN-X-1 |
| Concentrations in µg∙org-1 | ||||||
| Proteins *Lipids Carbohydrates | 30.01 ± 0.22 5.55 ± 0.04 5.40 ± 0.02 | 27.89 ± 0.19a 5.11 ± 0.03a 4.92 ± 0.02a | 37.89 ± 0.25c 9.76 ± 0.06c 8.04 ± 0.05d | 39.79 ± 0.34d 11.15 ± 0.14d 7.46 ± 0.03c | 41.12 ± 0.31e 11.90 ± 0.07e 8.70 ± 0.03e | 34.33 ± 0.25b 7.58 ± 0.06b 6.68 ± 0.05b |
| Percentages | ||||||
| Proteins | 44.54 ± 0.25 | 43.56 ± 0.17a | 53.36 ± 0.68d | 47.02 ± 0.52b | 54.11 ± 0.73d | 49.30 ± 0.47c |
| *Lipids | 8.24 ± 0.04 | 7.98 ± 0.04a | 13.74 ± 0.24c | 13.18 ± 0.23c | 15.66 ± 0.19d | 10.88 ± 0.11b |
| Carbohydrates | 8.01 ± 0.02 | 7.68 ± 0.03a | 11.32 ± 0.17d | 8.81 ± 0.06b | 11.45 ± 0.15d | 9.59 ± 0.09c |
Chlorophyll a and b and total carotenoids in juvenile Artemia franciscana
After 6 h of feeding, all organisms had higher pigment concentrations than the control (Table 5), but juveniles fed with TH-W-1 showed higher concentrations of chlorophyll a (0.482 ng Chla·µg-1 DW) and total carotenoids (0.345 ng TC·µg-1 DW; P < 0.05). Those fed with TE-S-1 exhibited the highest value of chlorophyll b (0.131 ng Chlb·µg-1 DW).
Table 5 Chlorophyll a, chlorophyll b, and total carotenoids in ng·µg-1 dry weight (DW) of the juveniles of Artemia franciscana at the beginning (0 h) and after (6 h) feeding them with the microalgae Thalassiosira weissflogii (TH-W-1), Chaetoceros muelleri (CH-M-1), Tetraselmis suecica (TE-S-1), and Nannochloropsis sp. (NN-X-1). Results are mean values ± standard error (n = 4).
| Determination | Initial | Control | TH-W-1 | CH-M-1 | TE-S-1 | NN-X-1 |
| Concentrations in ng·µg-1 DW | ||||||
| *Chlorophyll a | 0.010 ± 0.000 | 0.010 ± 0.001a | 0.482 ± 0.009e | 0.437 ± 0.002d | 0.248 ± 0.006c | 0.193 ± 0.002b |
| Chlorophyll b | 0.005 ± 0.000 | 0.004 ± 0.000a | 0.102 ± 0.004c | 0.081 ± 0.002b | 0.131 ± 0.004e | 0.121 ± 0.003d |
| *Total carotenoids | 0.050 ± 0.001 | 0.043 ± 0.001a | 0.345 ± 0.002d | 0.328 ± 0.001c | 0.229 ± 0.006b | 0.228 ± 0.004b |
Different letters indicate significant differences between treatments (P < 0.05). *Non-parametric test.
Discussion
Microalgae proximal composition, concentration of chlorophyll a and b, and total carotenoid content
As expected, diatoms present lower concentrations of organic matter than green microalgae because they possess frustules with higher percentages of inorganic matter. However, no trend has been observed in which proteins, carbohydrates, and lipids exhibited lower values in diatoms than in other species, as observed by Renaud et al. (1999). In this study, only the protein content was higher in green microalgae than in diatoms.
The protein content of TH-W-1 (244.70 mg∙g-1) was similar to the value of 289 mg∙g-1 reported by García et al. (2012). Regarding the protein content of CH-M-1, our value was lower than that reported by Carbajal-López (2008) for Chaetoceros calcitrans, while our values for TE-S-1 and NN-X-1 were higher than those reported by the same author (274.57 mg∙g-1 for TE-S-1 and 169.34 mg∙g-1 for Nannochloropsis oculata). These differences could be due to the different microalgae species, media (e.g., Carbajal-López [2008] used f/2 medium), or methodologies employed between studies.
Similarly, these reasons may also explain the differences observed in carbohydrate and lipid content. The carbohydrate content obtained in this study for TH-W-1 (185.57 mg∙g-1) was similar to the value of 207.00 mg∙g-1 reported by García et al. (2012) for the same species. On the other hand, Carbajal-López (2008) reported carbohydrate content of 42.55 mg∙g-1 for C. calcitrans, 22.25 mg∙g-1 for TE-S-1, and 18.96 mg∙g-1 for N. oculata, which are lower than those reported in this study. The lipid content of TH-W-1 (117.99 mg∙g-1) in our study was lower than that reported by García et al. (2012), which may also be due to the differences in culture conditions between studies (e.g., different media, temperatures, and salinities). However, the lipid concentrations of CH-M-1 and TE-S-1 in this study were higher than those of Carbajal-López (2008) for C. calcitrans (103.27 mg∙g-1) and TE-S-1 (86.63 mg∙g-1). Lastly, the lipid content of NN-X-1 in this study was similar to that reported by Carbajal-López (2008) for N. oculata.
In this study, chlorophyll a was the most abundant compound in all species of microalgae, while chlorophyll b was the second most abundant compound in green microalgae. These results agree with those of Jeffrey and Wright (2005). Although it was not evaluated in this study, chlorophyll c, in addition to the 2 chlorophyll types mentioned above, is found in many groups of marine algae, including diatoms, brown algae, and dinoflagellates (Zapata et al. 2006). In this study, the concentration of chlorophyll a in TH-W-1 (8.93 pg Chla∙ng-1 DW) was higher than those reported by Saxena et al. (2022), who recorded concentrations ranging from 2.79 to 6.01 pg Chla∙ng-1 DW for this species. Similarly, Saxena et al. (2022) reported chlorophyll a values that ranged from 2.60 to 4.16 pg Chla·ng-1 DW for Chaetoceros gracilis. These concentrations were lower than those recorded in this study (7.50 pg Chla·ng-1 DW for CH-M-1). The concentration of total carotenoids for TH-W-1 (1.96 pg TC·ng-1 DW) in this study was similar to that reported by Bhattacharjya et al. (2020) for Thalassiosira sp. (1.50 pg TC·ng-1 DW). The concentration of total carotenoids for CH-M-1 (2.98 pg TC·ng-1 DW) in this study was higher than that found by Goiris et al. (2012), who reported a value of 2.33 pg TC·ng-1 DW for samples of lyophilized biomass of C. calcitrans.
Few studies have reported chlorophyll b content in diatoms. However, Ju et al. (2009), who worked with Thalassiosira weissflogii, and Wang et al. (2019), who analyzed Phaeodactylum tricornutu, reported concentrations lower than those obtained in this study. In the case of Ju et al. (2009), these differences may be due to the different procedures used to obtain and analyze the samples. With regard to Wang et al. (2019), these differences may be due to the different species, culture media, and temperatures employed, as well as the different light/dark cycles or exposure to 5 p-chloroaniline concentrations.
The chlorophyll a content of TE-S-1 (12.59 pg Chla·ng-1 DW) was similar to the concentrations obtained by Abiusi et al. (2013), who cultivated the same species for 9 days using LEDs of different colors and reported values of 7.00 to 16.00 pg Chla·ng-1 DW. Nevertheless, the content of chlorophyll b (3.64 pg Chlb∙ng-1 DW) and total carotenoids (3.72 pg TC∙ng-1 DW) obtained in the present study were lower than those recorded by the authors mentioned above, who reported values ranging from 6.00 to 13.00 pg·ng-1 DW for chlorophyll b and 6.00 pg·ng-1 DW for total carotenoids.
Regarding the pigment concentrations, the chlorophyll a content (7.60 pg Chla∙ng-1 DW) for NN-X-1 obtained in this study was higher than that reported by Ra et al. (2018), who reported values of 4.00 to 6.00 pg Chla∙ng-1 DW for Nannochloropsis oceanica, although the value in this study was similar to that obtained for N. salina (6.00 to 10.00 pg Chla·ng-1 DW). Ra et al. (2018) evaluated the effects of mixed wavelengths of white and green light from LEDs on microalgae. However, the concentration of chlorophyll b (2.45 pg Chlb∙ng-1 DW) in this study was higher than that obtained by those authors, who reported chlorophyll b concentrations lower than 2.00 Chlb∙ng-1 DW in both species. Moreover, the concentration of total carotenoids (1.61 pg TC·ng-1 DW) in this study was similar to that reported by Goiris et al. (2012), who reported a total carotenoid concentration of 1.65 pg TC·ng-1 DW in N. oculata.
Temperature and light intensity are key factors affecting the productivity of microalgae (Hindersin et al. 2014). In addition, nitrogen and phosphorus supplementation influences the synthesis of biochemical components of cultured algae (Rasdi and Qin 2015). For example, nitrogen and phosphorus limitation in algal culture media promotes lipid accumulation (Franz et al. 2013), whereas excess temperature or light induces carotenoid synthesis (Panis and Carreon 2016). Diatoms in the exponential and stationary phases of harvest contain more fatty acids than green microalgae or blue-green microalgae (Wongrat 1995). In the case of carotenoids, some microalgae strains accumulate the highest cellular concentrations of carotenoids in the mid-late exponential phase of growth (Gómez-Loredo et al. 2016).
Proximal composition, chlorophylls, and total carotenoid content in juvenile Artemia franciscana
Juvenile A. franciscana fed with the isolipidic diets of TH-W-1, CH-M-1, TE-S-1, and NN-X-1 presented higher protein, carbohydrate, and lipid concentrations and percentages than those in the control. However, juveniles fed with TE-S-1 exhibited higher concentrations and percentages of proteins, carbohydrates, and lipids than those fed with the other microalgal species, which agrees with the proximal composition of TE-S-1. In contrast, juvenile A. franciscana fed with NN-X-1 presented the lowest concentrations of proteins, carbohydrates, and lipids per organism when compared to the juveniles fed with the other microalgae, which may be because Artemia nauplii cannot digest Nannochloropsis species because of their rigid cell walls (Gerken et al. 2013).
The protein percentage of the juveniles fed the TE-S-1 diet (54.11%) in this study was similar to that found by Maldonado-Montiel and Rodríguez-Canché (2005), who reported a percentage of 53.1% for adult Artemia sp. fed with the same microalgae. In another study, Shanmugam and Rajendran (2018) obtained 55.55% protein in adult A. franciscana fed Chaetoceros sp., which is higher than that found in this study with the microalgae Chaetoceros muelleri (47.02%). The lipid percentage reported by Shanmugam and Rajendran (2018) of 19.38% for adult A. franciscana fed Chaetoceros sp. was higher than that found in this study for juvenile Artemia fed with Chaetoceros muelleri (13.18%). However, these authors reported a lipid percentage (16.06%) in organisms fed with Tetraselmis sp., which was similar to that obtained in this study in juveniles fed Tetraselmis suecica (15.66%). Sánchez-Saavedra and Paniagua-Chávez (2017) reported a carbohydrate percentage of 18.83% for adult A. franciscana fed with Chaetoceros muelleri, which is higher than that obtained in this study for juveniles fed with the same species (8.81%). Nevertheless, Shanmugam and Rajendran (2018) reported a carbohydrate percentage of 15.11% (based on dry weight) for organisms fed Tetraselmis sp., which is similar to the value reported in this study (11.45%) in juvenile A. franciscana fed Tetraselmis suecica.
The total carotenoid content in A. franciscana juveniles in this study was higher than those reported by Cheban et al. (2020), who obtained values of 0.06 to 0.18 ng TC∙µg-1 DW in Artemia salina nauplii enriched with the microalgae Desmodesmus armatus, Chlorella vulgaris, and Dunaliella viridis for 24 h. In contrast, the concentrations in this study were lower than those obtained by Abdollahi et al. (2019), who reported a value of 0.88 ng TC∙µg-1 DW for adult A. franciscana enriched for 4 h with β-carotene from Dunaliella salina. No references were found reporting the chlorophyll concentration in crustaceans or possible functions. However, antioxidant activity that prevents oxidative DNA damage and lipid peroxidation is a beneficial effect of chlorophyll (Pangestuti and Kim 2011).
High-quality meals, such as Artemia enriched with microalgae, are crucial for the success of fish larvae cultures, as these diets provide the nutritional elements needed to support the lifespans, ideal growth, and immune systems of fish (Madkour et al. 2022). In this sense, Artemia juveniles enriched with carotenoids from microalgae, such as those evaluated in the present study, can also serve as food for ornamental fish, such as Xiphophorus maculatus, given that supplementing their diets with carotenoids improves coloration and mucosal immune responses (Abdollahi et al. 2019). In addition, Pérez-Rodríguez et al. (2018) studied the effects of feeding M. americanum larvae a diet of Artemia enriched with C. calcitrans microalgae, reporting that the overall growth, growth rate, and survival improved.
In conclusion, positive effects were observed in the proximal composition, concentration of chlorophyll a and b, and total carotenoid content of juvenile A. franciscana fed different microalgae species after 6 h. Organisms fed with Tetraselmis suecica exhibited the best results in terms of proximal composition and chlorophyll b content, while those fed diets of Thalassiosira weissflogii and Chaetoceros muelleri presented the best results in terms of total carotenoid and chlorophyll a content.
