Discretion
‘…Vendors Of Fruits, Clothing…May Sell In Private…’
(Mo’ed Katan 13b)
The Mishna states that professional animal trappers may trap [a large number of] animals on Chol HaMo’ed for the sake of the Festival (i.e., to sell for Festival use). However, in contrast to a non-professional who is permitted to perform a labor on Chol HaMo’ed in public, a professional must perform his work in private (i.e., out of public view). The Magen Avraham (Orach Chayyim 533:s.k. 9) explains that a professional’s work creates the appearance of labor performed for the weekday since it is performed on a large scale. Therefore, it must be performed out of public view.
Out Of Public View
The Mishna states a similar halacha with regard to a merchant selling his wares on Chol HaMo’ed. Even though a merchant may sell items on Chol HaMo’ed that are needed for Yom Tov, he must conduct his business in a discreet manner, e.g., at a remote location and out of public view. The Gemara explains that if one’s storefront faces the street, he may not leave the door open in its usual manner because that would attract too much attention (and there is a concern that observers will think that he is selling items for post-Festival use).
Perishables
The Gemara qualifies this halacha: A merchant selling perishable food (such as certain vegetables or fish) may sell his wares even in public. Since the food cannot last until after the Festival, it is obvious to an observer that it is being sold for Festival consumption and there is no room for suspicion or confusion.
Based on this, Rema (Orach Chayyim 533:4-5), citing the Mordechai, rules that in contrast to trappers of animals, a fisherman is permitted to fish in public view on Chol HaMo’ed since people will understand that he plans to sell the fish for Festival consumption.
The Magen Avraham (loc. cit. s.k. 10) disagrees and maintains that a fisherman is forbidden to catch fish in public – even though it is apparent that he intends to sell the fish for Festival consumption.
Modern Refrigeration
In Zichron Shlomo (Hilchos Chol HaMo’ed Ch. 5, Note 26) it is asserted that today professional fishing in public is forbidden even according to Rema. Since we now have the means to preserve fish (by freezing and canning), it is no longer evident that the fish caught on Chol HaMo’ed will be consumed on the Festival. [Selling fish, baked goods, vegetables and other perishables in public, however, is still permitted today because these items, when sold at retail, are usually purchased for immediate use, not to freeze or can.]