Research methodology remains same as regards to research design, sampling theory and so on. With each product the universe and sample frame changes and according to that sampling plan is to be selected. Which  fish products you are referring. For each major type of product different variables  exist. These have to be identified.

You have to also define what is consumer preference and what variables exactly you will measure.

The common mistakes ( Specially students) made by researchers is to jump straight to questionnaire before literature study , identifying research problem and what end results are required. Questionnaire is last stage of research design process.

The Survey form can have several types of questions. Responses on likert scale, multiple choice questions, yes-no type question or questions asking respondent specific choices and comments. Any good questionnaire should also have in end 1 or 2 open end questions where respondent can give you important feedback. Specially important for pilot testing stage. We should never go to field without pre tested questionnaire.

First think in the best advantage of the fish products. Try to measure the impact on the quality of life for clients. Analise 20/80 to get a good impact with little investment. Try to see the weakness of the fish product market. For example too expensive, 

For people or dificulties to store it, the fisch have also to be well