Slow-Cooker Sea Bass with Tomato-Fennel Relish Poaching fish is a smart use for your slow cooker. The wine mixture cooks for 2 hours to get hot and mingled before the sea bass is added to the slow cooker for 15 to 25 minutes. The relish, with its slightly acidic tomatoes, briney capers and crunchy fennel, is a great complement for the fish. This dish also makes a fantastic topper for salad greens. Garnish with additional fresh thyme sprigs, if desired.