This pie chart visualizes the distribution of fish species from a CSV dataset loaded via `d3.csv`. It uses `d3.nest()` to count occurrences per species, then `d3.pie()` and `d3.arc()` to generate the chart geometry, with `d3.scaleOrdinal` and `d3.schemeCategory10` for color encoding. The SVG rendering includes an interactive legend, and the code demonstrates a reusable pattern for pie charts with D3 v6.