Easy Fish Stew with Tomatoes and Fennel

Ingredients

• 2 tbsp olive oil
• 1 small fennel bulb, finely diced (about 2 cups), fronds reserved
• 2 carrots, finely diced (about 1 cup)
• 1 small onion, finely diced (about 1 cup)
• 1 1/2 cups water
• 1 796-mL can diced tomatoes
• 1 236-mL bottle clam juice
• 1 Yukon Gold potato, grated
• 1 400-g pkg frozen white fish fillets, such as haddock or tilapia
• 1/2 tsp salt