Mountain Stream Trout Co. agreed to buy "market size" trout from trout grower Lake Farms, LLC.Their five-year contract did not definemarket size.At the time, in the trade,market sizereferred to fish of one-pound live weight.After three years, Mountain Stream began taking fewer, smaller deliveries of larger fish, claiming thatmarket sizevaried according to whatever its customers demanded and that its customers now demanded larger fish.Lake Farms filed a suit for breach of contract.

1. Is the parol evidence admissible to explain the terms of this contract. Are there any exceptions that could apply?
2. What would be the impact of course of dealing and usage of trade on the interpretation of contract terms?
3. How could a party to a commercial contract avoid the possibility that a court will interpret the contract terms in accordance with trade usage?