The exemption from the overtime pay requirements provided by section 13(b)(4) of the Act extends to employees “employed in the * * * marketing * * * storing, packing for shipment, or distributing of any kind of” perishable aquatic product named in the section. An employee's work must be functionally so related to the named activity as to be, in practical effect, a part of it, and the named activity must be performed with respect to the perishable aquatic commodities listed in section 13(b)(4), in order for the exemption to apply to him. The named activities include the operations customarily performed in the marketing, storing, packing for shipment, or distributing of perishable marine products. For example, an employee engaged in placing perishable marine products in boxes, cartons, crates, bags, barrels, etc., preparatory to shipment and placing the loaded containers on conveyances for delivery to customers would be employed in the “packing for shipment” of such products. Salesmen taking orders for the perishable aquatic products named in the section would be employed in the “marketing” of them. Employees of a refrigerated warehouse who perform only duties involved in placing such perishable marine products in the refrigerated space, removing them from it, and operating the refrigerating equipment, would be employed in “storing” or “distributing” such products, depending on the facts. On the other hand, employees of a public warehouse handling aquatic products which have been canned or otherwise rendered nonperishable, or handling perishable products which contain substantial amount of ingredients not named in section 13(b)(4), would not be within the exemption. Office, clerical, maintenance, and custodial employees are not exempt by reason of the fact that they are employed by employers engaged in marketing, storing, packing for shipment, or distributing seafood and other aquatic products. Such employees are exempt only when the facts of their employment establish that they are performing functions so necessary to the actual conduct of such operations by the employer that, as a practical matter, their employment is directly and necessarily a part of the operations intended to be exempted (see, for some examples, § 784.155).