There is an increasing awareness of microplastics in the environment and their potential negative consequences for water security, biodiversity, ecosystem services, human health and wellbeing [1]. This awareness has spurred a surge in research on microplastics, including their occurrence and environmental distributions, chemical and physical properties, fate and transport [2], impacts on biota and ecosystems. Plastic materials are non-corrosive, durable, non-reactive, lightweight, and easy to handle, and due to their cheap manufacturing cost has made them a material of choice. Plastic production has increased substantially since large scale industrial manufacture started in the early 1950s. Almost all aspects of daily life involve plastics. In the European Union [3], for example, the main applications of plastics include: packaging (39.9 percent, much of which is single-use), building and construction (19.7 percent), automotive industry (8.9 percent), electrical and electronic (5.8 percent), agriculture (3.3 percent) and other (22.4 percent) applications (including consumer and home appliances, furniture, sport, health and safety).One of the most appreciated qualities of plastic products is their durability. However, this quality when combined with improper waste management leads to environmental contamination on land, in freshwater and in marine environments. Plastic products will degrade slowly over time, particularly when exposed to sunlight (ultraviolet radiation) and high temperatures. This degradation will lead to the breakdown of the material into smaller sizes ranging from the macroscopic to the microscopic and eventually to presently undetectable dimensions, the nanoplastics [4].

In aquaculture practice, fish feed is one of the crucial factors for the success of any aquaculture farm, where fishmeal is the base for such feeds. Fish feeds are integral to modern commercial aquaculture, providing the balanced nutrition farmed fish needs. Feeds can be found in different shapes, such as granules or pellets, based on the age and size of the fish [5]. Microplastics are generally characterised as water insoluble, solid polymer particles that are 5mm in   size.  A formal definition for the lower size boundary does not exist, but particles below 1mm are usually referred to as nanoplastic rather than microplastic [5]. Although microplastics are often detected in the environment, the risks they pose debated and largely unknown. One key challenge in assessing the risks of microplastics to humans and the environment relates to the variability of the physical and chemical properties, composition and concentration of the particles [6]. Micro plastics can exist in different forms, and their characteristics can vary depending on their source and environmental conditions. Micro plastic fragments typically range in size from a few micrometers (μm) to a few millimeters (mm). Pellets are often uniform in size and typically range from about 1 mm to a few mm in diameter, while fibers are usually longer and narrower compared to other microplastic types, ranging from around 10 μm to a few mm in length [7]. Their diameter can vary widely, from less than 1 μm to several micrometers. Primary microplastics refer to tiny plastic particle that are intentionally produced in their micro-sized form or are generated as a byproduct during manufacturing processes [8]. These microplastics are purposely produced with a particular purpose in mind, such as serving as powders for injection molding, abrasive particles, or resin pellets for the efficient movement of polymers between different manufacturing locations. Additionally, they can stem from the wearing down of large plastic objects during their production, usage, or servicing, such as the worn out of tires while driving or the wearing away of synthetic fabrics during washing. In general, the particles can take various forms, including microbeads, microfibers, and resin pellets [9].

Fish feed is mainly composed of marine trash fish, mustard oilcake, rice bran, wheat lower, molasses, and salt. Marine trash fish are mainly used to add protein, fat, phosphorus, and calcium to the fish feed content, while rice brans, wheat flowers, mustard oil cakes, and molasses are used for mainly carbohydrate and fiber contents. Trash fish, usually used in fish feed, are caught in oceans and seas10].

Studies revealed that marine water had been immensely loaded with microplastics [11] and a significant amount of marine fish species had been found contaminated with microplastic particles [12]. The size of detected microplastics from sea food based feed varied from 20 μm to 5 mm [13].  The predominant focus of numerous studies has been on investigating the presence of microplastics (MPs) in feed ingredients, with particular emphasis on fishmeal. Fishmeal is a crucial component incorporated into the diets of carnivorous marine species. Its content of MP can exhibit a range of values, spanning from 0 to 17.3 PL/g. The specific value within this range is contingent upon the fishing grounds from which the fishmeal is sourced, as indicated by various studies [14]. It is noteworthy to mention that the fishmeal obtained from fish captured in contaminated fishing regions exhibited the highest concentrations of MPs, thereby emphasizing the impact of marine pollution on the safety of feed constituents [15]. In addition, it is worth noting that plant based meals, which are frequently employed as substitutes for fishmeal in the production of animal feed, demonstrated similar levels of microplastics (ranging from 0.8 to 1.7 particles per gram) when compared to specific sources of fishmeal [16]. In addition to considering the characteristics and composition of the ingredients, it is important to acknowledge the presence of MPs in fish feeds which have been used in different life stages of cultured fishes [17].The main justification for the concern about microplastics in fish through feeding is the potential health risks they pose to both fish and humans. The health risks of microplastics to fish include reduced growth, increased stress, and increased mortality. Microplastics can also impact fish reproduction and may cause changes in fish behavior. In addition, microplastics can bioaccumulate and biomagnify in the food chain, meaning that they can become more concentrated as they move up the food chain. Microplastics have also been found to contain toxic chemicals and harmful bacteria, which can transfer to fish and humans [18]. The aim of this study is assess the level of microplatics contamination in commercial fish feed sold in Awka metropolis, Anambra State.

Study Area

This research was conducted in Awka, the capital city of Anambra State, and Nigeria, located in the southeastern region of the country. Awka is situated between latitudes 6°10'N and 6°15'N and longitudes 7°05'E and 7°10'E. Fish farming in Awka involves both small-scale and large-scale farmers, who utilize commercial fish feeds for the rearing of various fish species, particularly Clarias gariepinus (African catfish) and Oreochromis niloticus (Nile tilapia). The reliance on commercially available fish feeds makes it an ideal location for assessing the potential microplastic contamination in fish feeds.

Sample Collection

The fish feed samples for this study were sourced from some fish feed retailers in Awka. Three different feeds were selected namely Treatment A (Nigerian Feed), Treatment B (Foreign feed), and Treatment C (Nigerian Feed). Samples of each fish feed type were collected in triplicate, resulting in a total of 18 samples. The samples were analysed for microplastic contamination at Alpha Research Laboratory, Awka Anambra State.

Experimental Design

A completely randomized design (CRD) was used to compare the three treatments (A, B, and C). Each feed type (starter and finisher) was analyzed separately to observe the abundance, length, colour, morphology, and polymeric variation of microplastics. The data were statistically analyzed to assess significant differences between the feeds in each category.

Microplastics Analysis

The microplastic analysis in this study focused on five key parameters: abundance, length, color, morphology, and polymeric variation. Each parameter was systematically assessed to provide a comprehensive understanding of the microplastic contamination in the different fish feed samples.

Microplastic Extraction Protocol

Extraction was carried out using a two-step optimized microplastic extraction procedure, including chemical digestion and density separation. With this focus, the extraction protocol was adopted from Karami et al., 2017). 20 gm of fish feed (n = 6) was taken into a 250-ml conical flask. After that, 100 ml of a 10% KOH solution (1:10 w/v) was added to it and sealed for 96 h (4 days) under a laminar hood to complete the digestion. This solution was then separated and poured into another conical flask. 40 ml of saturated NaCl solution were then added to the solution and kept for 24 h (1 day) for density separation. Bone and flesh materials including the microplastics particles of fish feeds could be compromised by acidic digestion. Therefore, KOH digestion protocol was applied that might reduce the spectroscopic difficulty in identifying the polymeric composition. Again, fish feed is composed of complex biotic materials. Saline solution, e.g., NaCl, is denser than water and causes plastic materials to float to the surface. The supernatant was then vacuum filtered through 0.45 μm Whatman glass microfiber filter paper (GF/F Whatman TM, USA). These filter papers were then kept in Petri dishes, dried, and preserved for visual and polymeric inspection.

Visualization of Microplastics by Stereomicroscope

The conventional approach for identifying microplastics involves utilizing stereomicroscopy to visually detect them based on their size, shape, and color. In this study, all the filter papers were visualized by Leica EZ4E stereomicroscope (Leica, Germany) with 16x, 20x, 30x and 35x zoom on the basis of needs. The characterization of microplastics utilizing this technology primarily relies on their morphological and physical attributes, contingent upon the specific research objectives. The size categories of polymer species exhibit variation, spanning a range of 1–5 mm. This methodology does not furnish data regarding the specific identity of the polymer. Nevertheless, in order to assess the presence of potential plastic fragments, image processing software such as digital image J software was utilized to quantitatively determine the prevalence of microplastics. Microscopy is a process that may be influenced by subjectivity, tedium, and reliance on the observer. However, the utilization of automation and signal processing through image J software has the potential to mitigate these limitations. Nevertheless, this analytical technique lacked the ability to effectively differentiate microplastic particles from other anthropogenic synthetic particles. Therefore, in order to validate the existence of microplastic polymers, we further employed additional techniques such as FTIR spectroscopic analysis.

Polymeric Verification using FTIR

FTIR (Fourier Transform Infrared Spectrophotometer, Model no. IR Prestige-21, SHIMADZU, Japan) was utilized to validate the polymeric kinds of suspect microplastics. A representative number of samples were selected for characterization of microplastics by the FTIR. These microplastics were deemed to be indicative of the most often observed types of particles across all samples. Microplastics were evenly dispersed throughout a KBr crystal disc. Spectra were captured as the mean of 64 scans in the 4000-400 cm-1 spectral wave region at a resolution of 4cm-1. Each sample spectrum was verified by database from John Wiley & Sons, Inc.'s online spectral repository as well as by Jung et al., 2018.

Airborne Contamination Prevention

Concerted efforts were taken to reduce and eliminate airborne contamination during laboratory screening for MPs. Before starting, all glassware items were washed with mild detergent and thoroughly rinsed in running borehole water. Washed bottles and flasks were then autoclaved, clad in aluminium foil and stored in cupboards. All work surfaces were wiped down with 70% ethanol solution before the start of procedures. Specimen dissection, organ removals, decanting of KOH aliquots for digestion etc. were done in fume chambers with vacuum suction pumps. All persons involved wore cotton lab coats and latex (rubber) disposable gloves, Laboratory doors and windows were also shut, to reduce wind-borne contamination.

Statistical Analysis

Data were analyzed using one-way analysis of variance (ANOVA) to compare the microplastic content among the different treatments. Post-hoc test (Tukey’s HSD) was used to determine statistically significant differences between the means of the different treatments (P < 0.05). Statistical analyses were carried out using R statistical software (version 4.4.1, 2023).

Ethical Considerations

The feeds used in this study were commercially available products, and no live animals were involved in the research. All procedures were conducted following ethical guidelines for environmental research.

Microplastic Abundance in Different Fish Feeds

The microplastic abundance (particles per kg) in different types of fish feeds-Starter Feed and Finisher Feed-was analyzed across three treatments: Treatment A, Treatment B, and Treatment C. The results are presented in Table 1 below. The microplastic abundance varied significantly between the three treatments in both Starter Feed and Finisher Feed, with Treatment C showing the highest levels of microplastics across both feed types. In the Starter Feed, Treatment A recorded a significantly lower microplastic abundance (711 ± 1.00) compared to Treatment B (3733 ± 2.00) and Treatment C (9182 ± 1.53), with significant differences between the treatments (P < 0.05). Similarly, for the Finisher Feed, Treatment A (1006 ± 2.00) exhibited the lowest microplastic concentration, followed by Treatment B (3545 ± 1.00) and Treatment C (9401 ± 2.65), which were also significantly different (P < 0.05).No significant difference was observed between microplastic levels within the same treatment group across the Starter Feed and Finisher Feed, as indicated by the matching superscripts within each row (P > 0.05). This suggests that while the type of treatment significantly affects microplastic abundance, the feed type (Starter vs. Finisher) does not significantly alter the microplastic levels within each treatment group.

Table 1: Microplastic Abundance of Different Fish Feeds.

Means with the same superscript within rows are not significantly different at P > 0.05

Figure 1: Microplastic Abundance of Different Sampled Fish Feed.

Average Length Variations of Microplastics in Fish Feed

The average length of microplastics in different fish feeds as presented in table 2 below, shows significant variation across the three treatments. For both the Starter Feed and Finisher Feed, Treatment A had the longest average microplastic length (509 ± 1.00 µm for Starter Feed and 522 ± 2.65 µm for Finisher Feed), followed by Treatment B (318 ± 2.00 µm and 309 ± 6.78 µm, respectively), and Treatment C had the shortest average lengths (239 ± 1.53 µm for Starter Feed and 214 ± 2.99 µm for Finisher Feed). Significant differences in the average lengths of microplastics were observed between the treatments (P < 0.05). No significant differences were observed within Starter and Finisher of the same feed type, indicating that the average length of microplastics in the same treatment group did not vary significantly between Starter and Finisher feeds (P > 0.05).

Table 2: Average Length Variation of Different Sampled Fish Feed.

Means with the same superscript within rows are not significantly different at P > 0.05

Figure 2: Average Length of Different Sampled Fish Feed.

Color Variations of Microplastics in Different Fish Feeds

The color variation across the microplastics in different treatments shows significant differences. Treatment A consistently had higher proportions of blue microplastics compared to Treatments B and C for both Starter and Finisher feeds. Treatment B, on the other hand, showed higher amounts of brown microplastics, particularly in the Starter feed, where it recorded 57.50 ± 2.64%. White microplastics were most abundant in Treatment C across both Starter and Finisher feeds, indicating a dominant presence of white particles in this treatment. Red and pink microplastics were observed only in Treatment A, though in very small quantities, and absent in Treatments B and C. This variation in color distribution suggests different potential sources and degradation pathways of microplastics present in the feeds.

Table 3: Colour Variation of Different Sampled Fish Feed.

Means with the same superscript within rows are not significantly different at P >0.05

Morphological Variations of Microplastics in Fish Feed

The morphological variations  of microplastic in fish feed varies significantly.Treatment A higher in starter feed compared to other Treatments A and C .Fiber is more dominant with a record of  58.25 ± 1.70 in starter feed and in Treatment B of finisher feed with a record of is 42.0 ± 3.16, filament were recorded relatively high in Treatment A and B ,pellet were recorded in Treatment C, film was not recorded in Treatment A of starter feed and also in Treatment B of finisher feed, foam was also recorded.

Table 4: Morphological Variation of Different Sampled Fish Feed.

Means with the same superscript within rows are not significantly different at P >0.05

Polymeric Variations of Microplastics in Fish Feed

The Polymeric variation varies significantly among the three different Treatment, polyethylene terephyalate (PET) were recorded highest in starter feed of Treatment A with a record of 53.00 ± 3.65 and 44.00 ± 4.24 in finisher feed. Nylon was also recorded higher in Treatment C of finisher feed with a record of 12.25 ± 2.23, Polyethylene (PE) was noted followed by low density Polyethylene (LDPE) in most treatments.

Table 5: Polymeric Variation of Microplastic in Different Sampled Fish Feed.

Means with the same superscript within rows are not significantly different at P > 0.05

Key: PET - polyethylene terephthalate; PE-polyethylene; HDPE - high-density polyethylene LDPE - low-density polyethylene

Results of microplastic abundance demonstrates substantial variation in microplastic abundance across the three treatments (A, B, and C) for both Starter Feed and Finisher Feed. Microplastic concentrations in both feed types followed a consistent trend, where Treatment C exhibited the highest abundance of microplastics, followed by Treatment B, with Treatment A showing the lowest levels. These findings raise important concerns regarding the variability of microplastic contamination in commercial fish feeds and its potential implications for aquatic organisms and human consumers.The significantly higher microplastic abundance in Treatment C compared to Treatment A and Treatment B in both Starter and Finisher feeds suggests that certain fish feed production materials or handling processes may contribute to increased microplastic contamination [19]. The mean microplastic count in Treatment C for Starter Feed (9182 ± 1.53 particles/kg) and Finisher Feed (9401 ± 2.65 particles/kg) is alarmingly high, which could indicate more intense processing procedures or exposure to plastic materials during manufacturing or packaging. This is consistent with existing research that has identified feed production, packaging, and storage as potential sources of microplastic contamination in aquaculture feed [20].In contrast, the relatively lower levels of microplastics in Treatment A (711 ± 1.00 for Starter Feed and 1006 ± 2.00 for Finisher Feed) suggest that certain production protocols or raw material sources may be more effective at limiting microplastic contamination.The Implications of this findings for Aquaculture and Fish Health is that Microplastics in fish feed represent a direct route of exposure to aquatic organisms, with possible implications for fish health and, by extension, human consumers. Studies have shown that microplastics can accumulate in fish tissues and organs, causing a range of physiological effects, including oxidative stress, inflammation, and disruption of normal growth and development [21]. The high levels of microplastic contamination in Treatment C, particularly in finisher feeds, could pose a significant risk to fish, as this is the feed consumed during their final growth stages prior to harvest.

The absence of significant differences in microplastic abundance between Starter and Finisher feeds within the same treatment group (P > 0.05) suggests that the contamination levels are consistent across different feed formulations within the same production system. This is an important finding, as it indicates that the issue of microplastic contamination is not feed-type specific but rather treatment-dependent. Hence, the same level of scrutiny should be applied to both types of feed to ensure the safety and quality of aquaculture inputs [22].The ecological impact of microplastics in fish feed extends beyond the immediate effects on fish health. Microplastics are known to adsorb and concentrate various environmental pollutants such as persistent organic pollutants (POPs) and heavy metals [23]. Once ingested by fish, these pollutants may bioaccumulate, potentially affecting fish populations and food safety for human consumers. The findings of this study suggest that fish exposed to high levels of microplastics, especially in Treatment C, may face increased risks of ingesting not only microplastic particles but also the associated toxic chemicals.Moreover, given the increasing consumption of aquaculture products globally, the presence of microplastics in fish feed raises significant concerns for public health. Fish represent a critical source of protein for millions of people worldwide, and the transfer of microplastics and their associated contaminants through the food chain could have serious implications for human health [24].

Length of Microplastics in Fish Feed

Microplastic size and length varies in different types of feed, i.e from feed to feed .The longest microplastic was found in Treatment A while the shortest was found in Treatment C .The size variations in different feeds could be attributed to grain size of the feed types, packaging materials as well as the components of feed materials from various sources .Microplastics can be harmful to fish, particularly when they exceed 100 μm in length. Particles within this size range can accumulate in the gastrointestinal tract, causing blockages and digestive issues, which may lead to reduced feeding ability and growth retardation [25]. The analysis of microplastic length variation in different sampled fish feeds reveals significant differences between the treatments (A, B, and C) for both Starter Feed and Finisher Feed. The results show that microplastic length is inversely related to the concentration of microplastics in the feed, with Treatment A consistently exhibiting the longest microplastic particles and Treatment C having the shortest. These findings suggest that microplastic contamination is not only more abundant in some treatments (as seen in Table 1) but also smaller in size in treatments with higher contamination levels [26]. The significant difference in microplastic length between treatments suggests that the processes responsible for the introduction of microplastics into the feed might affect both the number and the size of particles. Treatment A, which had the lowest microplastic abundance, exhibited the longest average particle lengths, measuring 509 ± 1.00 µm for Starter Feed and 522 ± 2.65 µm for Finisher Feed. This may indicate that microplastics in Treatment A come from a less intense mechanical process, or perhaps from larger plastic sources that degrade less readily into smaller fragments [27].

In contrast, the smaller microplastics observed in Treatment C, with average lengths of 239 ± 1.53 µm (Starter Feed) and 214 ± 2.99 µm (Finisher Feed), may be due to more aggressive degradation processes or exposure to a wider array of smaller plastic debris. Previous studies have shown that smaller microplastic particles can result from greater environmental or mechanical degradation, such as through the increased use of machinery or exposure to high temperatures during feed production [28]. The Implications of this on Fish Health and the Environment is that the size of microplastic particles can significantly influence their biological impact. Smaller particles, such as those observed in Treatment C, have a higher surface area-to-volume ratio, which can increase their capacity to adsorb and concentrate harmful chemicals such as persistent organic pollutants (POPs) [29]. Furthermore, smaller microplastics are more likely to be ingested by a broader range of aquatic organisms, including smaller fish and invertebrates. This increases the risk of microplastic particles entering the aquatic food chain and causing bioaccumulation of toxicants [30].

Larger microplastics, as seen in Treatment A, may pose a lesser immediate risk in terms of ingestion by smaller organisms, but they can still be ingested by larger fish species, leading to potential physical blockages or other internal damage. Although the longer microplastic particles in Treatment A may represent lower contamination levels overall, their ingestion could still pose a risk to fish health, particularly in species that consume larger particles or are exposed to these microplastics over long periods [31]. The consistency in microplastic length between Starter and Finisher feeds within the same treatment group (P > 0.05) suggests that the production processes for each treatment do not significantly alter particle size between the two feed types. This is an important finding because it indicates that the length of microplastic particles remains stable within the same production method, regardless of whether the feed is for starter or finishing phases of fish development. However, this also means that the risk posed by smaller particles in Treatment C or larger particles in Treatment A persists throughout the entire feeding cycle [32].

Colors of Micro Plastic in Fish Feed

Color variation is a distinctive indicator of rising demand and the usage of a wide range of plastic products in daily life, which produces significant amounts of plastic waste. Total of five different colors where found in the sampled fish feed which includes blue, brown, red, pink, and white. The blue, white and the brown color were found to be dominant [33]. The color of the microplastic is an important aspect of characterization of the fish feed. These colors where found present both in finisher feed and starter feed. Similar results were evident in Yao et al., [34] who observed eight several colors including rarely found red colored microplastics in fish feed and shrimp feed. Rahman et al., [35] found black, blue, translucent and brownish color in cat fish feed assessed. Color variations may attract fish species especially when choosing the prey and the predator fish could mistakenly ingest these colored microplastics as thinking of their feed [36]. So identifying the color variation is important. Microplastic colors can originate from additional pigments added during plastic production or from color changes arising from sunlight exposure and chemical reactions in the environment (Zhao et al., 2022). According to Walkinshaw [38] blue and red microplastic particles are non - natural organic pigment derived from anthropogenic activities. White microplastic can come from microplastic that have undergone a photochemical process that causes the loss of color pigment in the microplastic [39]. Brightly colored microplastics, particularly those in red, blue, and green, are considered more dangerous due to their faster degradation into harmful microplastics compared to black, white, and silver plastics. Darker colors absorb more light, causing slower photoaging, but color can also impact other aspects of plastic degradation and microplastic formation [40]. Colors found in microplastics provide important information about the potential sources, environmental behavior, and ecological impact of plastic pollution. The color of microplastics can influence their visibility to organisms, their degradation rates, and their composition [41].

The analysis of color variation in microplastics across different treatments of sampled fish feeds provides valuable insight into the possible sources, characteristics, and degradation pathways of microplastic contamination. The significant differences observed in the distribution of microplastic colors between the treatments indicate distinct contamination patterns and suggest varying origins or production processes for the feed materials.  [41]. In both the Starter and Finisher feeds, blue microplastics were most abundant in Treatment A (47.75 ± 2.22% in Starter feed and 41.25 ± 2.21% in Finisher feed), while significantly lower proportions of blue particles were found in Treatments B and C. The higher prevalence of blue microplastics in Treatment A suggests the possible use of blue-dyed plastic materials in the production or packaging of the feed. This could also be indicative of a specific type of plastic waste that is commonly found in materials, such as fishing gear or certain packaging materials [42].Brown microplastics, on the other hand, were most abundant in Treatment B, particularly in the Starter feed (57.50 ± 2.64%). The dominance of brown particles in Treatment B may suggest different environmental sources of contamination or degraded products that contribute brown-colored fragments, such as ropes or plastic containers used in aquaculture practices. The significant difference between Starter and Finisher feeds in this treatment implies that brown microplastic contamination might be more prevalent during the early production stages or when the feed is designed for juvenile fish [43]. White microplastics were most abundant in Treatment C, with concentrations reaching 65.85 ± 0.74% in Starter feed and 63.00 ± 2.94% in Finisher feed. This high proportion of white particles suggests that the contamination in Treatment C likely originates from clear or white plastic materials, such as plastic bags, foams, or packaging. The near-equal distribution of white microplastics between Starter and Finisher feeds indicates that the contamination source remains consistent throughout feed production and use, irrespective of the feed type [44].

Red and pink microplastics were slightly present in Treatment A, although in much smaller amounts compared to other colors. The presence of red microplastics in the Starter feed (7.30 ± 0.46%) and pink microplastics in both Starter (2.09 ± 0.02%) and Finisher feeds (22.50 ± 3.10%) suggests potential contamination from specific sources, such as fragments of fishing gear, buoys, or consumer products that commonly use red and pink dyes. The absence of red and pink particles in Treatments B and C indicates that these colors may be tied to particular plastic materials or feed handling processes used exclusively in Treatment A[45]. The variation in microplastic color is not just a cosmetic difference, but it can also have ecological and biological implications. Certain colors of microplastics, particularly blue, white, and red, have been shown to be more attractive to marine organisms due to their resemblance to prey or natural food items (Ugwu et al., 2021). For instance, studies have indicated that blue and white microplastics are more likely to be ingested by fish and other aquatic organisms, leading to increased exposure to plastic debris and associated toxicants [46]. The high prevalence of white microplastics in Treatment C, therefore, raises concerns about potential ingestion by fish in aquaculture systems, which could result in physical damage or the introduction of harmful substances leached from the plastics. Similarly, the presence of blue and red microplastics in Treatment A could increase the likelihood of ingestion, especially in species that are visually attracted to such colors [46]. Also the color variation observed across the treatments are of ecological and environmental concern which likely reflects different sources of microplastic contamination during the feed production process or from environmental exposure. The consistency of certain colors, such as the predominance of white microplastics in Treatment C and blue microplastics in Treatment A, suggests that specific types of plastics are being introduced into the feed supply chain. This could result from the use of certain plastic materials in packaging, storage, or transportation, or from environmental contamination in areas where the feed ingredients are harvested or processed [46].

Morphological Variation in Fish Feed

The morphological variation in the fish feed occurs in varying proportion filament, pellet, film, foam and fiber were the observed morphotype. Filament were found higher in Treatment B of the starter feed accounted for 41.75 ± 3.30 but were absent in Treatment C of both starter feed(0.00 + 0.00) and finisher feed recording (0.00 ± 0.00). A high range of pellet was found in Treatment C of Starter feed (30.00 ± 3.74) and finisher feed with a range of 22.75 ± 2.98 there were predominantly no record for Treatment A and B of starter feed and finisher feed. Pellets are primary MPs produced by ultrafine grinding in mills and are widely  used in cosmetics and other personal-care products, primarily in small sizes [47].The average size of pellets in personal care products such as sunscreens is between 0.06 and 0.8 mm ( Sun et al. 2020). The presence of film were predominantly found in Treatment C with a record of 40.00 ± 2.58 in starter feed, there were relatively no records for Treatment A of starter feed and Treatment of the finisher feed. Films are also irregular, but thinner than fragments and possibly flexible [48]. Foam was found higher in Treatment A and B of the finisher feed with a record 41.00 ± 2.5 and 32.25 ± 2.06 relatively, while significantly low record was found in other Treatment of both starter and finisher feed .Foam Evoke From polystyrene, expanded or extruded (sometimes erroneously put together under the trade name styro-foam), although other foamed plastics exist in the market. Fiber are recorded the most dominant in Treatment A and B of the starter feed (58.25 ± 1.70 and 50.50 ± 2.88 respectively) followed by Treatment B of the finisher feed with a record of 42.0 ± 3.16. This result agrees with Fibers, being most abundant shape in this study, are reported to cause more harm to aquatic organisms than other Microplastics shapes  [49].

Polymeric Variation of Microplastic

Microplastics exhibit diverse polymeric variations, the polymer type of some selected samples from each morphotype for fish feed were identified using FTIR analysis. The FTIR characterization process is capable of identifying functional groups in compounds through the interpretation of infrared light signals sent by chemicals in the sample to the FTIR instrument [50]. Five different polymers were identified by FTIR in all types of fish feeds e.g. nylon, 6, polyethylene terephthalate (PET),  polyethylene (PE), high density polyethylene (HDPE),low density Polyethylene. The Polymeric features nylon -6, was found high in Treatment C of the finisher feed with a record of 12.25 ± 2.23 followed by Treatment A of the starter feed ( 11.50 ± 2.08) , Treatment B was relatively low. Specifically nylon-6 is noted for its presence in fish feeds, which can affect fish health through ingestion. Polyethylene terephyalate (PET) was found to be the most abundance in Treatment A and B of the starter feed with range of 53.00 ± 3.65 and 52.00 ± 3.16 and Treatment A of finisher feed with a record of 44.00 ± 4.24, Treatment C were relatively low in both starter and finisher feed .Polyethylene (PE) was recorded high in Treatment C of the starter feed and significantly low in other Treatments. PE, is translucent, semi-rigid, tough, and has good conductivity and chemical resistance. Available in three commercial grades and used in several applications (automotive, patio furniture, bottles, films, tapes, webbing straws, and appliances). PP products can undergo similar degradation processes to PE and generate MPs [51].

High density Polyethylene was recorded high in Treatment B of the finisher feed with a record of 10.00 ± 2.94 and its presence in Treatment A and C of both starter and finisher feed were recorded predominantly low. HDPE is a highly crystalline polymer with a linear chain produced by low pressure polymerization. Its applications include bottles, large containers, drums, fuel tanks, pipes, wrapping flms, and crates [52]. Low density Polyethylene were found to be absent in Treatment A and B of the starter feed and also in Treatment B of the finisher feed , it was also found in Treatment C of both starter and finisher feed with a range of 13.75 ± 1.71 and 16.0 ± 2.96 respectively. LDPE chain structure are highly branched and is a product of a non-catalyzed high-pressure polymerization. Its applications include packaging, bottles, plastic bags, clothes, water tanks, plastic furniture, and flms.  These polymers are generally used in food and beverage packaging, wrapping cosmetic items, houseware, food containers, and shopping bags [53].

Microplastic contamination in fish feed presents a significant environmental and health concern. Studies reveal that all types of fish feeds are contaminated with microplastics, with concentrations ranging from 550 to 11,600 particles per kilogram. This contamination not only affects farmed fish, which can ingest up to 268 microplastic particles over their lifecycle, but also poses risks to human consumers through the food chain. The presence of various polymers, such as polypropylene and polyethylene, highlights the urgent need for improved monitoring and regulation in aquaculture practices to mitigate these risks and ensure food safety. It can be concluded that microplastic contamination could be reduced significantly if precautions are strictly followed in fish feed preparation for all stages.

Recommendations

Microplastics in fish feed pose significant risks to both aquatic life and human health. Studies reveal that farmed fish can ingest substantial amounts of microplastics through contaminated feeds, with concentrations reaching up to 11,600 particles per kg 15. These microplastics often originate from marine sources and agricultural practices, highlighting a critical pathway for environmental contamination.

Given the potential risks associated with microplastic contamination in fish feed, it is crucial for future research to investigate the sources of microplastics in aquaculture feeds and identify effective strategies for reducing contamination. Feed manufacturers should consider revising production practices, packaging materials, and storage conditions to limit exposure to plastic materials. Furthermore, regulatory frameworks should be established to monitor and control microplastic levels in fish feed to ensure the safety of aquaculture products. In addition, further studies should explore the long-term effects of chronic exposure to microplastics in fish, focusing on the potential for bioaccumulation and trophic transfer through the aquatic food web. Understanding the full scope of microplastic contamination, from feed to fish to human consumers, is essential for safeguarding the sustainability and safety of aquaculture operations. Also, collaboration with scientists from other fields is essential to develop strategies for reducing microplastic release into the environment.

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