Pearl brothers

Two lizardmen swam along the seabed of a relatively shallow section of ocean, often pausing to open up oysters and check them for pearls. They were brothers; Kaj was the older of the two by a few years, with green scales and a proportionally longer tail. Lek was fairly similar, though he was shorter and had a yellow tint to his scales. Both shared a passion and talent for freediving that had led them to become pearl divers for their tribe, which happened to be close enough to the ocean that such a thing was feasible. Having each been at this for over a decade, they had impressive breath holding abilities: Lek could manage about 16 minutes, and Kaj a little over 20!
Right now, they'd been underwater for 8 minutes, and while only a few pearls had found their way into Kaj's bag, they were still enjoying themselves. Lek tapped Kaj's shoulder to get their attention, and pointed up to indicate he'd be heading up for air. Kaj nodded and decided to follow, both lizardmen soon catching their breath at the surface.
Only now did it occur to them how late it was, the sun starting to set. "Oh, we should probably get back, huh?", Kaj suggested.
"Yeah, getting kinda tired. Sucks that we didn't get much today."
They were quite a distance from shore, but could still see it, and were good enough swimmers that it wasn't much issue. Some time later, much of it being spent underwater, they'd returned to the land, and after a few minutes' rest they set off for home. It wasn't all that far, about a couple miles, though it was nearly night by the time Kaj and Lek had returned. They'd hand in the pearls tomorrow; for now, they relaxed in their hut as they prepared for bed.
"You ever thought about getting into alchemy?", Lek asked. "Turning into something aquatic would certainly make our job easier."
Kaj shook his head. "Never been a fan of... Potions, and all that. Just doesn't seem right to me. Besides, I kind of like holding my breath."
"Then I'll look into it. I bet you'll change your mind."
"I probably won't... Good night."
"Good night."
Both lizardmen settled into their beds, and, worn down from the day of swimming, it wasn't long before they fell asleep.

Kaj found himself at the mouth of a cave, the path ahead descending underwater. He'd been sent here to get something, and while he couldn't quite remember what it was, he was certain he'd know it on sight. Holding his breath, he dove in, swim deeper and deeper in, soon losing sight of the surface he'd entered through. This place seemed to be draining his oxygen; he already felt the need to breathe, but he couldn't leave empty-handed.
In just a few minutes, Kaj began to struggle, and he puffed out a bit of air to relieve some tension from his lungs. Oddly, his air came out as a single large bubble, about half the size of his head, but he had no time to dwell on that. Now starting to puff his cheeks, he swam and swam, another sizable bubble blooping away every now and then.
Eventually, he came across a large chamber, but by now it was too late. Kaj's lungs burned, his vision starting to blur, and he realized he'd pushed himself too far. He was going to drown in this cave! Kicking his legs and covering his mouth, he tried to rebreathe by deflating and reinflating his cheeks, but it didn't help, and he soon couldn't hold his breath any more. The lizardman's hands flew from his face as his mouth opened wide, exhaling all the air he had left in an enormous bubble that looked to be bigger than himself. Gurgling and flailing in desperation, he tried to grab at the bubble for a couple seconds as it floated out of reach, before his hands went to his neck as he gasped, his grip doing nothing to hold back the water rushing down his throat...

"Gah!" Kaj woke up from his nightmare, panting briefly before calming down. It wasn't uncommon that he'd dream about being underwater, as he'd spent a significant portion of his life below the waves, but nightmares like that were unusual. He looked over at Lek to make sure he hadn't woken them, and they seemed to still be asleep. Sighing, Kaj lay back down to get back to sleep. It certainly took more time than earlier, but he managed it, and his dreams for the remainder of the night were the typical nonsensical mishmash, nothing really standing out.

Morning came, and the brothers soon awoke. They greeted each other, had some food, and delivered what few pearls they'd gotten the day before. This time, they were going to be taking the day off; as much as they enjoyed their job, they still needed a break from it every now and then. Lek took some time to study alchemy, though it turned out more complicated than he'd expected. Kaj busied himself by wandering around a forest near the village, occasionally diving into lakes and exploring their depths to help train his lungs, for what little it would do.
The next night came and went, and it was back to work for the two lizardmen. Kaj grabbed his pearl bag and dive knife again, and him and Lek set off for the ocean again.
"So, Lek. Did you actually try learning about alchemy?"
"Yeah, but man, it's harder than I expected. Can't tell the difference between bloodgrass and devilgrass, and that's apparently pretty basic. I thought they were the same thing!"
"Heard it was complicated. Keep at it, I'd say, you'll probably get a feel for it eventually."
Finally back at the beach, Kaj and Lek wasted no time diving back into their home-away-from-home and resuming their hunt for pearls. Like last time, it wasn't going that well, and it was starting to be frustrating. Their search took them to a much deeper area, the bottom being about 120 feet down, with large columns of rock extending upward, some of them being tall enough to reach above the surface. Something on the seabed caught Kaj's eye: A clam that was far bigger than the others, to the point where he'd fit inside it if it were closed, which it wasn't. It sat wide open, and sitting in it was a massive pearl! Kaj's eyes lit up as he swam straight for it, before Lek quickly grabbed his tail to stop him. Lek shook his head and pointed up with two fingers, which the brothers had agreed would mean that one wanted to surface along with the other for whatever reason, typically to say something as it would be difficult to get any kind of message across while underwater.
At this depth, it took some time to surface, but they got there without any issue. "What, why'd you stop me?"
"We can't do that big clam. I've heard of past divers getting trapped and drowning in ones like that."
"You actually believe that? It's just some weird rumor someone started."
"Maybe, but I don't want to find out!"
"Well... According to the rumor, are they always alone?"
"...Yeah?"
"Then if we go together, we'll be fine."
"I... Y-you're probably right."
Kaj and Lek both held their breath again and dove back down, eventually floating next to the huge pearl and sinking down to stand next to it. Lek was still nervous, but as nothing seemed to be happening, he started to feel a bit better. Kaj gave him a reassuring look, and reached down to grab the pearl.
Just a moment after he touched it, the clam started to quickly close! Lek yelled out bubbles, but that and getting their tails out of the way were all either of them had time for before the clam slammed shut, trapping them inside. While there wasn't any outside light any more, it turned out that the huge pearl was glowing, so the lizardmen could still see. Kaj bent over somewhat, rubbing his head as the shell had hit it, the space inside the clam not being tall enough for him to stand upright.
The two looked at each other fearfully. While they certainly had a long time before they'd run out of breath, Lek was on the verge of panicking, now swimming against the upper shell in an attempt to push it open. Kaj joined in, able to put much more force into it by virtue of being able to stand at the same time, but even their combined efforts were for nothing.
Now Lek was starting to lose it, frantically banging on the shell and calling for help. Kaj put a hand on their chest to try to calm them down, and, now mostly having their attention, spoke as clearly as he could. "Cablm doblwn. Wble cabln fiblgurble thblis oublt." Lek nodded after taking a moment to completely interpret what Kaj had said, already looking a fair bit more calm.
Still holding onto his dive knife, Kaj tried to jam it into the tiny crack between the two halves of the clam's shell, which took a few seconds, but eventually he managed it. Bracing his feet against the top shell, he pushed down on his knife as hard as he could, with nothing seeming to happen. He motioned for Lek to join in, which he did, and the combined efforts of both of them...
...Snapped the knife in half. It was certainly a lot harder to keep from panicking, now, with what seemed to have been their best chance no longer being an option. Kaj looked at what remained of his broken knife... It might still be usable, but certainly not for getting out of here. Meanwhile, Lek had gone back to freaking out, now trying to wedge his fingers into the tiny crack that was far too small for them, while Kaj was pushing against the top again.
Their struggles dragged on and on, and eventually the brothers had been trapped for a full 10 minutes, both of them now puffing their cheeks and blushing from strain. All the fear and wasted effort was more quickly burning through what oxygen they both had, but the bubbling was hardly an issue; the bubbles that they were losing were gathering on the ceiling, forming an air pocket that was slowly expanding. After finally noticing that, Lek started breathing from it, only able to get his nostrils inside. Kaj had decided to at least give a shot at prying open the clam with his broken knife, but now he couldn't even get it set in place.
With another few minutes, Kaj and Lek were starting to get purple blushes, their lungs burning. Bubbles streamed from Kaj's nostrils and continued to slowly expand the air pocket, which wasn't really much help for Lek any more, who panted and nervously watched Kaj continue to struggle with his broken knife, neither really seeing anything better to do.
Yet another minute, and Kaj covered his mouth, starting to shiver from the lack of oxygen, his blush shifting to a blue tone. He joined Lek in breathing from the air pocket, the latter of them now lightheaded from breathing the stale air for so long. They looked at each other again as it started to dawn on them that they likely wouldn't be getting out of this...
Kaj's lungs weren't satisfied with getting almost no oxygen from the nearly worthless air pocket, forcing to pant more and more deeply. Eventually he and Lek happened to inhale too much at the same time, thinning out the air to such a degree that both had their nostrils submerge, water getting sucked in instead. They coughed heavily, and while Lek managed to go back to breathing through his nostrils, Kaj didn't, gasping and just getting more water. 
It was like the nightmare he'd had, but he wouldn't be waking up this time, and had to endure every second of it. He grabbed his neck as he choked, getting air not really being an option any more. "KABLJ!", Lek yelled, though Kaj was too focused on the pain to really notice, thrashing about in the small space, accidentally hitting Lek a few times. One of those hits was to his stomach, knocking the wind out of him and causing his instincts to force him to gasp, now joining Kaj in drowning.
After about 30 seconds of gurgling, Kaj managed to regain some level of focus. The water rushing in and out of his lungs combined with the sight of his brother drowning gave him an adrenaline rush like no other, and with strength he didn't know he had, Kaj pushed against the top shell once again. This time, it was actually working! The seam between each shell slowly grew wider, and when the gap was about a foot wide it seemed that the clam recognized its defeat, the top shell flying open to release the drowning lizardmen.
With each second bringing the two of them closer to death, Kaj had no time to waste, grabbing Lek and starting to swim up with him in tow. Lek quickly realized he was free, and Kaj released him as he started trying to swim. They still had a long way to go, but the distance was the only thing holding them back, now.
With the last bubbles leaving their lungs, their aquatic chokes continued to ring out, now sometimes joined by hiccups. Their progress to the distant surface was painfully slow, only managing 2 or 3 feet a second, and while they weren't sure whether their bodies would be able to hold out long enough, there was no way they would just give up. Even as each one's blue blush started to spread over the rest of their face, and Lek's eyes began to go unfocused, their panicked swimming wasn't getting any slower.
60 feet remained. The choking was stopping, slowly being replaced by simple heavy panting, though the hiccups became a bit more common.
30 feet left. Kaj and Lek were both entirely blue in the face, now, and the dire lack of oxygen was causing their bodies to start shutting down, feeling increasingly sleepy as their vision dimmed.
10 feet. The brothers were going numb, their swimming getting sloppy as they now fought to stay awake, Kaj's purple tongue lolling out...
Neither immediately realized when they breached the surface, flailing about in an attempt to continue swimming up. They'd stopped trying to breathe at this point, but when it finally occurred to them that there was air, water erupted from each lizardman's mouth and nostrils, and desperate, hoarse gasps followed. Kaj and Lek thrashed as they did their best to not sink underwater again, slowly making their way to a nearby rock pillar, which Kaj climbed onto first and helped Lek up, before they both collapsed, coughing and panting, still spitting up some water.
Several minutes passed before either could speak, still breathing heavily. "...Ffucking...huu...T-told you...", Lek managed to say. Kaj tried to respond, but fell into a coughing fit as his lungs ridded themselves of the last few drops of water. When they'd both returned to breathing normally, Kaj finally tried again to respond to what Lek had said. "Sorry I didn't believe you."
"It's alright. Like I said, wasn't really sure about it myself."
Both of them sat up. "...So I guess we're the only ones to survive one of those, huh?", Kaj said.
"Yep. Sorry about your knife, by the way."
Only now did it occur to Kaj that he hadn't brought what was left of his dive knife up with him, and he'd even lost his bag at some point as well. "It's fine, I can get another."
Not long after that, the exhaustion of the prior events finally started to hit them, each coming down from a massive adrenaline rush. Not even able to say anything, they fell backwards, soon passing out and sleeping off the partial drowning they'd both endured.