Characteristics and differences of microplastics ingestion for farmed fish with different water depths, feeding habits and diets

Highlights

• First report of the relationship between MPs accumulation and water depth, feeding habits and diets.

• The bottom-dwelling omnivorous fish had the largest ingestion of MPs accumulation.

• Fish size and diets were linked to differences in MPs accumulation.

Abstract

Microplastics have become a potential hazard to the quality and safety of aquatic products although there are few reports on microplastics distribution related to water depth, feeding habits and diets in aquaculture ponds. In this study, five aquaculture fish species (Ctenopharyngodon idella, Hypophthalmichthys molitrix, Cirrhinus molitorella, Oreochromis niloticus and Pelteobagrus fulvidraco) were selected and their accumulation of microplastics was measured and classified. We found that the water depth, feeding habits and diets led to large differences in microplastics accumulation. The bottom-dwelling omnivorous fish had the largest ingestion of microplastics and ranked as P. fulvidraco>O. niloticus>C. molitorella，the herbivore C. idella in the middle benthic layer and the upper-layer filter-feeder H. molitrix had the lowest ingestion. The detection frequency in the gastro-intestinal tracts for C. idella, H. molitrix, C. molitorella, O. niloticus, and P. fulvidraco were 93.33%, 91.67%, 87.50%, 92.86%, and 90.91%, and detection frequencies for gills were 86.67%, 100%, 87.5%, 100%, and 81.82%, respectively. Fibers presented the dominant shape (91.92%) and blue was the primary particle color in the majority of the samples (77.39%) and 0.5–2 mm particles dominated. The plastics were composed of olefins, acrylic, rayon, polyester, polyethylene and polypropylene. Our study first reported the relationship between MPs accumulation and water depth, feeding habits and diets in aquaculture ponds, which also has a certain correlation with the fish size.

Introduction

Fish products are an important high-quality protein source and aquaculture is an effective means to achieve human nutritional goals and food security ( [1], [68]). China possesses the largest aquaculture area in the world with production in 2020 at 52.24 million tons, which is the only country in which aquaculture production exceeds that of wild fishing [74]. However, all types of fisheries are currently threatened with pollution and in particular the presence of microplastics (MPs) that was first reported in 1972 [10], [12], [60], [9]. Plastic outputs have also been increasing and this is directly related to elevated amounts of pollution by these materials [43], [81]. Physical forces such as wave action and chemical forces including solar radiation led to the disintegration of plastics into small pieces < 0.5 mm to become MPs [21], [25].

MPs are new pollution types that have paralleled technological developments and have far-reaching influences [26], [29]. The MPs pose an even greater harm to animals [52] such as intestinal wall damage and reproductive and behavioral abnormalities [3]. For instance, exposure of brine shrimp (Artemia parthenogenetica) to MPs resulted in deformed and disorderly intestinal epithelia [69]. Ingestion of 100 nm polystyrene particles by the zooplankton Daphnia magna inhibited their growth and development and decreased their reproductive ability [8]. The number and size of oocytes produced by female oysters exposed to MPs were significantly smaller than those were not exposed. In addition, sperm motility rates were significantly lower than controls and the growth rate of offspring larvae was also significantly slowed [62]. In additionally, the plastics themselves are often chemically modified using a variety of additives and amendments [5] and these compounds have included teratogens and carcinogens. These additives will be continuously released into the environment via their disintegration and will most likely have a profound impact on the environment [24]. Fish ingest food from the water and this commonality belies the wide variety of digestive and feeding organs that have evolved [59]. Pond aquaculture systems have relied on polyculture to foster an ecologically balanced environment that increases the diversity and the stability of the system [27]. The MPs are also present in these farm ponds, although their effects are not completely understood and further research is needed to guide farmers to rational polyculture and healthy consumption by consumers ( [18], [38], [72], [73]).

In this study, we examined 68 fish samples from five different fish species (Ctenopharyngodon idella, Hypophthalmichthys molitrix, Cirrhinus molitorella, Oreochromis niloticus and Pelteobagrus fulvidraco) that display different water depth and feeding habits in a typical aquaculture farm. We comprehensively explored the degree of their MPs contamination and correlated this with feeding habits and with the number, color and size of the MPs materials in the gills and digestive tracts. We examined the five fish species that were the primary components of the system to determine whether all were exposed and affected to the same extent. These data will provide a theoretical basis for future ecological assessment and healthy breeding in aquaculture farms.