THE EFFECTS OF MICROPLASTIC INGESTION ON THE FEMALE REPRODUCTIVE SYSTEM OF THE CRYPTOBENTHIC GOBIID FISH, EVIOTA EPIPHANES, USING ARTIFICIAL TROPHIC TRANSFER

Abstract

Plastic pollution is one of the most pervasive anthropogenic stressors faced today by aquatic fauna. One of the greatest threats that plastic pollution is associated with is ingestion, particularly microplastic (<5 mm) ingestion, which has been shown to lead to various pathologies associated with internal organ systems and physiological pathologies. The work reported on here attempts to better understand the relationship between microplastic ingestion and any subsequent morphological pathologies observed, and to take steps to develop more efficient methodologies to promote standardization across the study of microplastic effects on aquatic organisms. The first part of this thesis reports on an investigation to develop an effective artificial trophic transfer method using Artemia salina. Live A. salina nauplii were fed 6.10-μm polystyrene microplastic beads at three different time intervals (two-, four-, and six-hours) and in two treatment groups (aeration and no-aeration). Artemia salina had a significantly increased ingestion of microplastics in the aeration treatment (average of 20 to 24 microbeads per gut) when compared with no-aeration treatment (average of 1 to 10 microbeads per gut) but no significant difference of microplastic ingestion was observed across the time intervals in the aeration treatment group. The next experiment used these findings to implement indirect ingestion of 6.10-μm polystyrene microplastic beads to Eviota epiphanes, a small, cryptobenthic, Hawaiian reef fish. This study was designed to help elucidate if indirect ingestion of microplastic, through the consumption of microplastic-fed A. salina, resulted in accumulation and/or alteration of liver and gonadal morphology. Individual fish were maintained separately within a custom-made microplastic accommodating aquarium system, known as the Microplastic Experimental Aquarium System (MEAS). This system prevented microplastic cross-contamination between the treatment groups and inhibited microplastic pollution into the environment. In the MEAS, the experimental group of E. epiphanes were fed live A. salina that had in turn fed on microplastic beads. The control group of E. epiphanes were fed live A. salina that had not been exposed to the microplastic beads. Neither microplastic accumulation nor observable morphological differences were found in a detailed histological comparison of gonad and liver morphology between experimental and control fish. These findings suggest that E. epiphanes may not be particularly vulnerable to microplastics around the size range of 6.10-μm, at least over short periods of time. However, the possibility of deleterious effect(s) caused by the exposure of small-sized aquatic fauna to smaller-sized nanoplastics is currently unknown and may play an important role in trophic transfer through the lower end of aquatic ecosystem food chains.