## 1 Introduction  
Photosynthetic microalgae are valuable renewable resources for a diverse range of industrial applications, including food, unraceuticalals, pharmaceuticals, animal feed, biofuels, and biochemicals [1, 2]. Astaxanthin (AXT), a prominent secondary ketocarotenoid pigment found in microalgae, has gained considerable commercial importance in the health food supplementation, cosme, and aquaculture industries owing to its potent antioxidant bioactivity and distinctive reddish coloration [3, 4, 5]. Furthermore, AXT exhibits substantial potential for therapeutic effects, including cardiovascular protection, immune modulation, antiaging, and anticancer effects [6, 7]. _Haematococcus lacustris_ (formerly referred to as _H. pluvialis_[8]) is a rich source of AXT (~5% of the dry cell weight) and is extensively cultivated to meet growing market demands [9]. This microalgae accumulates AXT during its physiological and morphological transformation from vegetative cells to dormant cysts under unfavorable culture conditions [10]. AXT biosynthesis is linked to a complex defense mechanism that aids microalgae cells in the management of oxidative stress [11]. Various stress-based approaches, including intense light irradiance [12], high salinity [13], nitrogen deficiency [14], elevated temperature [15], phytohormone supplementation [16], mechanical compression [17], and hydrostatic pressurization [18], have been employed to enhance AXT production. However, the development of an environmentally friendly and effective AXT induction strategy remains a substantial challenge in industrial microalgal biotechnology [6]. Electric stimulation techniques have been effectively applied to enhance the biosynthesis of various organic products in individual electroactive, acetogenic, and methanogenic microorganisms, as well as in mixed cultures [19; 20]. This process is potentially sustainable because it uses renewable electrical energy at ambient pressure and temperature, thereby eliminating the need for chemical additives. The resulting renewable electricity-based chemicals (referred to as e-chemicals [21]) include ethanol, butanol, 3-hydroxypropionic acid, 1,3-propanediol, isopropanol, formic acid, butyric acid, and acetate. However, research on microalgae in this context remains limited, and the effect of electric treatment varies considerably based on the species and physiological cell status. _H. lacustris_ exhibits a complex life cycle consisting of five distinct cell types: red dormant cysts, germinating cysts, green biflagellate cells, green palmella cells, and greenish-brown palmella cells [22; 23]. [PERSON] et al. [24] subjected biflagellate cells of _H. lacustris_ to a strong current intensity (100 mA) for a brief duration (1 min), resulting in a considerable increase (20%) in cell number density, although this treatment did not cause alteration in the AXT content compared to that of untreated controls after subsequent photosynthetic cultivation for seven days. Conversely, [PERSON] et al. [25] continuously electrotreated _H. lacustris_ biflagellate cells at a relatively low intensity (30 mA) for an extended period (two days), resulting in a 36.9% higher AXT content (6.0 mg/g cell) than that of the untreated cells. Aerobic electrochemical conditions [26] can generate reactive oxygen species (ROS), which act as signaling molecules to help microalgal cells adapt to stress and activate AXT biosynthesis [3]. However, severe cell damage occurs in electrotreated cells, including cell-wall and cytoplasm separation along with the extracellular secretion of biomaterials, which is likely due to the excess generation of oxidizing radicals triggered by electrotreatment and a significant drop in pH through water electrolysis [25]. To address these challenges, this study aimed to investigate the technical feasibility of mild electrotreatment (30 mA or below) to stimulate AXT accumulation in _H. lacustris_ while maintaining cell stability under photosynthetic culture conditions.