Final answer:
Tunas and lamnid sharks possess tissues that enable them to regulate their body temperature above that of the surrounding water, which classifies them as endothermic, unlike most other fish species.
Step-by-step explanation:
The statement that tissues in tunas and lamnid sharks are endothermic is true. While most fish are ectothermic, meaning their body temperature is regulated by the surrounding water, there are exceptional cases among fish such as tunas, swordfish, and certain species of sharks.
These exceptions show some warm-blooded adaptations and possess the ability to elevate their body temperature above that of the surrounding water, allowing for increased metabolic rates and more efficient muscle functioning, among other advantages. This type of thermoregulation is a characteristic typically associated with endothermic animals like mammals and birds.