**1. Introduction**

The microalgae *Isochrysis zhanjiangensis*, a marine single-cellular golden-brown flagellated species isolated from Nansan Island of Zhanjiang of Guangdong Province, China [1], is an important species in the aquaculture economy and commonly used in the fodder industry and various mariculture systems [2]. Due to the small size, fast-growing, cellulosefree cell walls, and nutrient-richness, especially in polyunsaturated fatty acid (Omega-3), chlorophylls, and carotenoids, *Isochrysis zhanjiangensis* has been mass-produced for feeding fish, shrimp, shellfish seedlings, as well as larvae of a variety of aquaculture animals [3,4]. In particular, *I. zhanjiangensis* is used as a food supply worldwide during broodstock hatchery conditioning. Additionally, it is especially used to culture suspension-feeding larvae and early juvenile bivalve mollusks, because of its nutritional properties that support shell growth and the high survival rates when used as a mono-species diet [5,6].

The growth and propagation of microalgae are affected by several environmental factors, such as temperature, salinity, light, and pH. Light, the main source of energy for algae growth, is one important key factor in regulating its growth and development [7]. Photosynthetic microorganisms do not utilize the whole solar spectrum but only a fraction of it, in particular from 400 to 700 nm. The absorption wavelengths of visible light by algae and plants are mainly concentrated in the blue-violet light region of 400–510 nm and the redorange light region of 610–720 nm. However, the wavelengths absorbed by microalgae differ

**Citation:** Lv, B.; Liu, Z.; Chen, Y.; Lan, S.; Mao, J.; Gu, Z.; Wang, A.; Yu, F.; Zheng, X.; Vasquez, H.E. Effect of Different Colored LED Lighting on the Growth and Pigment Content of *Isochrysis zhanjiangensis* under Laboratory Conditions. *J. Mar. Sci. Eng.* **2022**, *10*, 1752. https://doi.org/ 10.3390/jmse10111752

Academic Editors: Sang Heon Lee and Azizur Rahman

Received: 10 October 2022 Accepted: 10 November 2022 Published: 15 November 2022

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

according to species [8]. Several investigations have been focused on either the single or combined influence of light quality (meaning the different wavelengths which are absorbed by water to various extents) [9–12], light quantity (different light intensities) [13–19], and light periodicity (different photoperiods) [20–23], thus indicating that illumination is a complex external factor for microalgae cultivation. Moreover, researchers have found that light quality plays an important role in regulating the growth and development, morphology, photosynthesis, and metabolism of algae [24–27]. For instance, red light is an efficient light quality for the growth of *Arthrospira (Spirulina) platensis*, while it has a significant inhibitory effect on the chlorophyll content [28]. The cultivation of chlorophytes under a mix of green and blue LEDs may prove optimal for growth, biomass productivity, pigments, proteins, and lipids [29–32]. Green light enhanced growth rates, protein, and lipid contents in *Brachiomonas submarina*, and pigment content in *Kirchneriella aperta*. Highand low-intensity green LEDs enhanced lutein biosynthesis compared to red or blue LEDs in *B. submarina* and *Scenedesmus obliquus* [33,34]. High-intensity blue LEDs increased the carotenoid zeaxanthin, and white light was optimal for phycobiliprotein in *Rhodella* sp. and fucoxanthin content for *Stauroneis* sp. and *Phaeothamnion* sp. [33]. Although, the use of any white light sources (fluorescent lamps, RGB LEDs, and white LEDs) for the cultivation of green algae seems to not affect growth. A species-specific response of algae to light intensity has been described in *Desmodesmus quadricauda, Parachlorella kessleri*, and *Chlamydomonas reinhardtii* [35]. In *P. kessleri* cells, the concentration of pigments decreased with increasing light intensity, a response found not only in the genus *Chlorella* [13,36–38], but also in other green algae [39].

Light quality, intensity, and photoperiod also affect the growth, biochemical composition, and physiology of *Isochrysis* sp. [40–42]. Microalgal pigments change with algal variety. Therefore, the influences of different light qualities on the physiological properties of algae, such as growth, photosynthesis, and cellular metabolism, are diverse [43]. The ability of the microalgae to utilize different light qualities is determined by this composition of pigments in their cells, and different pigments absorb different light qualities. The growth and development of microalgae and the generation of metabolites are related to light quality, and the light quality that is most suitable for the growth of one microalgae species may not be suitable for another [33]. Therefore, it is of great significance to explore the optimum light quality for the growth of *I. zhangjiangensis*. Thus, this study aims to examine the effects of different LED light qualities on the productivity, chlorophyll, protein, and carbohydrate content of *I. zhanjiangensis* in indoor culture. Our results will aid the optimization of the light conditions for the growth of *I. zhanjiangensis*. Additionally, the results will provide the basis for the optimization of microalgae propagation in indoor conditions and other systems that require artificial illumination in general.
