Conclusion

It is hard to arrive at a firm conclusion because it all depends on your perspective.  To determine if fish is meat to you, then you need to choose your perspective and assess it.  Unfortunately, many of these perspectives are correct in their own regard as they created the definition of meat for their perspective, much like you deciding if the term "truck" refers to only trucks, or trucks and SUVs.

There are many arguments that occur because people are looking at things from a different perspective, and everyone believes that their perspective is the correct one.  The only way to truly understand is to make sure that both people are using the same ruler.  Is it 3-feet or one yard?  Many people hate to arrive at the conclusion of "everyone wins," but in this situation that may be the case.  If a person's definition of meat excludes fish, and you take the biological approach to determination, then you both will undoubtedly disagree.

Many people use simple approaches to determine if fish is meat, such as: is it the flesh of an animal?  If it is, then it is meat.  Depending on your purposes, this approach may be perfect for you, but there are others out there that must consider many other things before they can arrive at a determination.

If the terms "meat" and "fish" are differentiated by language, which is the case with the Latin word "Carne" used in the Catholic Canon Laws, then it is no fault of the authors that, when "Carne" is translated into a different language, it takes on a different meaning.  The only thing that can be done is to say: It means meat, but excludes fish.