Betta Fish: Help is something wrong with my betta?

Is there something wrong with Bibble? The first two pictures are from the 13th of March and the last two are from today. Is it an abscess? Or is he bloated? Please help. I’ve only had them for about 3 months. He’s eating and acting normal but is this something I should be worried about?

Tank size: 275 litres (±70 gallons)
• Heater and filter: Yes
• Tank temperature: 25–26°C
• Water parameters: Ammonia 0.02 ppm, Nitrites 0 ppm, Nitrates 0 ppm, pH 5.8
• Tank age: Newly set up and cycled
• Fish age: I’ve had bibble for 3 months
• Water changes: Weekly, 25–50% per change
• Tankmates: 3 kuhli loaches, 7 corydoras, and a large population of ramshorn snails
• Feeding: 5–6 times per week with 1–2 fasting days (Hikari food) and occasionally bloodworms
• Decorations and plants: Natural plants and driftwood