Analysis of population size and food preference of <em>Pterygoplichthys multiradiatus</em>: focus on microplastics in streams with different human impacts

Abstract

The pollution and accumulation of plastic in the environment, along with its mass production, has grown significantly in recent decades. Plastic can be very persistent due to its durability, and strength. Furthermore, they can disperse to any habitat under the influence of wind, rain, and runoff. In addition, as a direct result of the widespread use of plastics in modern society, plastic waste accumulates, especially in urbanized areas where it often ends up in watercourses and is eventually transported to river bodies. Pollution from fluvial plastic transport, particularly from rivers, remains relatively understudied compared to marine plastic litter. However, recent research efforts to quantify plastic pollution and its effects have begun to focus on freshwater systems because rivers ultimately discharge their waters into the ocean. However, given that research on riverine plastic debris transport is a relatively young science, the need to emphasize the urgency of increasing global knowledge about plastic pollution in freshwater ecosystems is necessarily important.<br /> <br /> Most rivers with high concentrations of plastic debris are located near urban areas, presenting significant risks to aquatic life and biodiversity. Because of this, urban river segments are particularly susceptible to invasion by exotic species, which is common in locations with poor water quality. Introducing exotic species into urban water bodies is a common problem in many cities worldwide. Exotic fish can displace native species, disrupt the ecological balance and contribute to the spread of diseases and parasites. This can be problematic as some exotic fish, such as species in the families Poeciliidae, Cichlidae, and Loricariidae, can be particularly prolific and can expand rapidly, which can further increase their negative impact on the local ecosystem. <em>Pterygoplichthys</em> is a genus of freshwater fish family Loricariidae, commonly known as plecos or armored catfish. These fish are native to Central and South America and are found in rivers and lakes in the region. However, some members of the genus <em>Pterygoplichthys</em> have become invasive species in some parts of the world. Such is the case with <em>Pterygoplichthys multiradiatus</em>, a freshwater fish species popular with aquarists because it controls algal growth in aquariums. It is believed that <em>Pterygoplichthys multiradiatus</em> may compete with other native fish species for resources and habitats and alter algal communities and other aquatic organisms. Similarly, in Puerto Rico, government agencies, such as the Department of Natural and Environmental Resources, have classified plecos as an invasive species, which has caused severe damage to economic sectors such as agriculture and fisheries, as well as adverse effects on the island's biodiversity that represent a threat to the public health of the surrounding communities.<br /> <br /> <em>Pterygoplichthys multiradiatus</em> has detritivorous habits and demersal distribution adapted to attach to the substrate to consume algae, organic sediments, and small invertebrates in river bodies. This may increase the risk of plastic ingestion for bottom-dwelling species as they decompose into smaller fragments that are easier to consume and have a higher probability of carrying contaminants. Therefore, given the accumulation of anthropogenic waste reaching rivers, this has resulted in an increasing generation of plastic debris in a variety of sizes to which aquatic biological organisms are exposed. However, as large plastic waste is broken down into small particles by photodegradation and biodegradation, these plastic fragments, form microplastics.<br /> <br /> However, because populated islands are also potential sources of plastics, the Caribbean islands are a vulnerable point in the degradation of biodiversity resources, including terrestrial and aquatic ecosystems. In Puerto Rico, for example, which along with other islands is part of the Greater Antilles archipelago in the Caribbean region, there is little assessment of plastic contaminants in aquatic ecosystems. Therefore, the present study highlighted the contamination by plastic waste, particularly by microplastics, which were found in the gastrointestinal tract of freshwater fish <em>Pterygoplichthys multiradiatus</em>; being an exotic and invasive species able to tolerate disturbed ecosystems and with a wide distribution in urban streams of Puerto Rico. Because of this, the objectives of this study were: 1) to estimate the population size of <em>Pterygoplichthys multiradiatus</em> and to identify variations in the abundance of the species between urban and suburban streams, in relation to various land use scenarios; 2) to use the<em> P. multiradiatus</em> as a model organism, to determine, quantify and identify the types of microplastics found inside the gastrointestinal tract of the organism; finally, 3) to quantify the degree to which direct exposure to plastic affects the amount ingested by the plecos, in order to know and determine if the impact produced by these residues is a component of the main diet of the species.