Sharks - One of the most misunderstood creatures.
Firstly, They're Smart
Like most fish, sharks are viewed by humans as creatures devoid of thought and feeling, simply because they (literally) can't express it in the same way that mammals do. They're social learners, problem-solvers, maintain complex relationships, have distinct personalities, and are even self-aware. The range of intelligence, both social and otherwise would actually put sharks above dogs and cats in intelligence, and their relative brain size reflects this. If you think that dogs and cats are sentient creatures deserving of love and respect, then you should think the same, if not more, of sharks (and many fish too.)
Secondly, They're Relatively Harmless
Sharks have inhabited Earth since 450 million years ago, long before humans even existed. We're nowhere near their natural prey, and as a result they don't view us as lunch. Perhaps if literally starving, but a vast majority of shark attacks are either due to confusion or curiosity. Splashing at the top of the water will trigger instincts they've developed for hunting seal, which can provoke a bite, or they may simple wonder what you are. Without any other way to feel or taste you, they might bite you. Even if they do, they don't like the taste of human, and will almost always not continue past that. The rumor that they can smell blood from a mile away is technically true but misleading. Your blood would have to travel to their nose first, and studies have shown they're not even attracted to human blood. Finally, they're mostly peaceful to humans anyways. I'm sure you've seen plenty of people swim with them, and statistically you're more likely to die from a vending machine than a shark. The increase in attacks over the years reflects more how we've very aggressively encroached their natural habitat for recreation.
So why do their faces look so empty?
Well, it's not their fault.
Sharks are aquatic predators, and of a completely different class than mammals. Therefore, it's really no surprise that they don't express themselves the same way we do. Their faces literally lack the muscles which would be required to make facial expressions, but that doesn't mean they're not expressive. Instead, sharks express themselves mostly through body language and behavior.
Pisciquus were inspired by sharks, and how misunderstood they are, and so I copied this into their biology. Pisciquus lack the ability to make expressions as well, and are even rather monotone, but they also express themselves in their body language and some noises. Below is detailed how so, some of which is inspired by sharks, and some of which is simply made-up.
Pisciquus Body Language & Noises
Happiness and Contentment
Having no subconscious movement at all - A pisciquus which is just standing there, with no extra motions, is a content or indifferent pisciquus. This should be the default if there's no stimuli which would trigger any particularly strong feelings.
Wagging the tip of their tail - Swaying the tip of their tail slightly side-to-side is a sign of subtle happiness or excitement in a pisciquus. Things like talking to their friend, eating good food, or doing something they generally enjoy. The rest of the tail may move a bit as a result, but the defining factor to look for is that the motion doesn't go very far in either direction.
Pupils becoming smaller - When a pisciquus views something it finds attractive, pleasant, or exciting, then its pupils will become smaller to increase its focus. This stems from a natural hunting instinct, which helps them focus in on prey, so expect to see it during hunting as well (which makes sense anyways, since getting food is exciting.)
Leaving Mouth Open and Drooling - This is a sign of pleasure or extreme happiness in a pisciquus. This usually happens when something absolutely delights them or makes them very excited. Think things like a good present or a trip to a theme park.
Fear and Discomfort
Pupils becoming larger - A pisciquus's pupils will enlarge when they're in an environment which makes them feel anxious or unsafe. This stems from a natural protective instinct which helps increase their depth of field to spot and avoid dragons (their natural predators) or other threats. Expect this around areas or things they're unfamiliar or uncomfortable with, but also in awkward social situations.
Lowering head, tensing body, and backing up to a wall - This is a natural defensive stance a pisciquus takes when they feel directly threatened. It primes them for a lunge, to run, or to defend themselves, and cuts off as many blind-spots as possible.
Growling - This is simply a pisciquus's way of saying "Go away!" or "stay away from me!" This is mostly commonly seen when defending their territory from other pisciquus, or keeping other creatures at bay which scare them but aren't actively hunting them. Traditionally, it was a warning of violence, but modern pisciquus tend to growl anytime someone is bothering them, even if they're just annoyed and not intending to actually escalate things.
Flicking tail fully side-to-side - While short wags are a sign of happiness, long swings which go from one extreme to the other, regardless of speed, are a sign of general discomfort, annoyance, or unhappiness. Expect this from a pisciquus which is mildly uncomfortable, annoyed, or is just in a generally bad mood.
Pupils dilating back and forth - Pupils which are pulsing, growing a little large and smaller in short intervals are a sign of embarrassment. Think of it like the pisciquus equivalent of blushing, since they cannot.
Love and Affection
Purring - When a pisciquus is being affection with someone it loves, especially physically affectionate, they'll emit a faint low purring sound. This is the same whether the affection is with a family member, a mate, or just a very close friend.
Staring - Pisciquus are curious creatures, and it's extremely common for them to stare at people they like, analyzing their features, whether that be because of a personal bond or because there's something interesting or attractive about them. The difference between staring, and simply looking at someone, is that they'll do it even if that person is not actively engaging with them, and outside of simply examining them upon first meeting.
Licking - Like many creatures, pisciquus can express affection in the form of licking with their long tongue. Though, unlike many licking creatures, this is purely reserved for very intimate relationships, since it represents a high level of trust in the wild, since pisciquus have quick powerful jaws and can become cannibalistic if starving.
Soft biting - When a pisciquus is being extremely intimate, it will often administer "love bites". Unlike the previous examples, this behavior is resolved solely for mates, and is part of the typical ritual. Due to their strength and sharp teeth, a pisciquus will need to be careful about this if they're intimate with a species that's less durable.
Anger and Hatred
Slapping tail on ground - Sharp, vertical movements of the tail, usually resulting in the ground being slapped, are a general sign of anger. The strength with which they do this is usually indication of the severity, with minor anger being small taps, and severe rage being powerful whacks.
Chittering - Usually a sound made while actively chasing prey, or when threatening someone. Either way, this sound is closely related to immediate violence.
Avoiding eye contact - As a contrary to staring, a pisciquus will actively avoid looking at or making eye contact with someone they dislike, or otherwise find repulsive.