Possible Clues:

• Right at the beginning, complaining of feeling ill
• The fish may be first-rate, but it's enough to make one sick
• For the sick cockney, getting a taxi
• Unwell, in poor condition
• The fish may be first grade, but it's enough to make one sick (6).
• Barrier put up right from the start for the sick
• Sloth and fish not doing too well
• Even first-class fish may make one sick
• The fish may be first-rate, but will make you sickly
• Even first-rate fish may have one sick