The warm current shimmered ahead of me like a river of light. It rose from a fault line where the vent fields gave way to smoother stone, carrying a slow drift of heat that felt almost like breath. The water tasted faintly metallic, touched with the sweetness of plankton bloom. It was not Harbour’s steady warmth but a living one, the kind that changed from moment to moment.

I followed it until the dark opened into a basin. The light that reached me there was not from stone or flame but from bodies. Hundreds of needle-finned swarm fish moved through the water in a single silver shape. Their reflections flickered in tight waves, scales flashing in rhythm. They turned as one. When one bent its tail, every other followed, the formation folding like fabric caught in a current.

For a moment, I watched without hunger. The movement was hypnotic. They breathed together, pulsed together, every fin catching the same beat. Then the current brushed my gills, and the heat sharpened the ache inside me. Instinct returned. Food was food.

I sank lower and waited for their pattern. The school swirled in slow spirals, feeding from the plankton fog that clung to the warm flow. Each circuit lasted eight steady beats. On the ninth, they shifted direction and began again. Predictable. If I could time the break, I could strike through the seam of the spiral and catch two or three before they closed again.

I let the current push me close. The warmth hid my own pulse. My fins flexed against the stone. The swarm curved above, the shimmer of their bodies folding inward to begin another pattern. I counted the beats in silence.

One. Two. Three.

Their movement quickened near the vent mouth where the current squeezed. Four. Five. Six.

I waited for the turn. Seven.

The outer ring opened. Eight.

I launched.

My body cut through the plankton like a knife through cloth. The first row of swarm fish scattered in confusion. The second row folded around me in reflex. I bit the nearest body clean through and felt the rush of heat fill my throat. Before I could swallow, a dozen more shapes closed around me. Their fins sliced across my scales in a dozen shallow cuts. The water thickened with blood and motion.

The school had no leader. It did not need one. Every fish followed the pulse of its neighbours. My entry had changed the rhythm, and they adapted in a heartbeat. The circle collapsed. I was inside a living net.

I twisted, but their bodies pressed from all sides. Thin mouths nipped at the soft joins near my gills. The water around me churned so thick with silver that my sonar clicks came back as noise. I slashed with my fins, but every cut brought another wall of bodies. I needed space.

The vent bubbles.

I remembered the ones I had stored two days earlier in the small crevice near Harbour’s mouth. Pockets of gas, sealed under stone, harvested from cracks that breathed too weakly to burn. I had learned to trap them behind a film of mucus and rock dust, a weapon for future use. I still carried two along my lower fin.

I forced myself still. The swarm pressed closer, tightening the ring. When the first mouths touched my flank, I drove the fin forward and broke the seal. The bubble rose through the water like a white seed. When it reached the tight cluster above me, it burst.

Hot gas ripped through the formation. The pressure startled the fish. Their perfect rhythm broke in an instant. A hundred small bodies scattered in every direction.

I used the gap to strike. My jaws closed on two of them before the others even found direction. Flesh tore easily. I swallowed fast, not caring about taste. The rush of heat steadied my thoughts. The school had lost its rhythm. I moved through the confusion like a blade through loose sand, snapping at the edges, driving the rest into the walls of the basin.

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For a few minutes, the water was chaos. Every flash of silver was another opening. I hunted until the pain in my side began to fade behind the pulse of victory.

Then the current changed.

The school did not flee. It regrouped.

The survivors twisted into a tighter shape, smaller but sharper, and began to move again. The spiral returned, not eight beats this time but six. The pattern had evolved. My first attack had taught them.

I hovered at the edge of the basin and studied the new formation. The spiral now pulsed faster, every rotation marked by a quick inward flick. They were testing for my movement. Every few seconds one fish darted toward where I had been, as if expecting me to strike again. They were learning from my rhythm the same way I had learned from theirs.

Good.

I let the current push me closer again. The new pattern turned clockwise instead of counterclockwise. Their centre glowed faintly with trapped plankton light. They were guarding the core of the swarm, feeding from the centre out. That was their weakness. If I could shatter that core, their formation would collapse a second time.

The vent bubbles were gone. I would have to improvise.

I slid along the stone until I found a crack where the vent gas escaped in thin threads. The heat burned against my belly, but the pain was manageable. I lowered myself until the gas pooled under me, trapping it between my body and the rock. It would build for a few breaths before escaping. Enough for one burst.

I waited until the swarm’s spiral passed above. On the sixth beat they turned inward again. I struck the vent with my tail and forced the gas upward.

The plume hit the centre of the spiral and tore it open. Fish scattered, but not as wildly as before. The new rhythm held them together in smaller sub-rings. They had divided themselves into groups, each mirroring the other. Clever.

I darted toward the nearest sub-ring and bit down. The group broke apart, but another closed from behind, cutting off my escape. Their bodies pressed tight, using my momentum against me. Their tails whipped in unison. The strikes were not strong, but the repetition hurt. I slashed with my fin ridges, shearing scales, and the ring loosened enough for me to slip free.

The second sub-ring adjusted instantly. They had learned to let the others take the first blow, then close after the strike. I could not break them all by strength. I needed to make them break themselves.

I dove low, stirring the silt until the water clouded. The swarm fish relied on sight and vibration. If I could blur one and confuse the other, they would turn on one another.

The first pulses of sonar came back scattered through the cloud. The fish clicked to each other, trying to re-establish their rhythm. I answered with a short pulse of my own, copied from their pattern. The signal bounced between them. The closest ring turned toward me, but the second mistook the echo as a call from the first.

The two collided.

Silver shapes crashed together, tails flaring, fins tearing skin. The water boiled with confusion. I slipped between them, taking bites where I could. The taste was sharp and sweet.

By the time the silt cleared, the basin floor was littered with motionless shapes. The survivors fled into the dark beyond the vent’s light, their pattern finally broken.

I drifted in the centre of the hollow, panting through my gills. Blood—mine and theirs—hung in thin threads that curled upward toward the ceiling. The water was warm and thick with the smell of iron.

The ache in my muscles spread from jaw to spine. Each twitch of my tail sent a sharp sting through the half-healed wounds from the eel. I had won, but not cleanly. The swarm had fought with thought, not just instinct. It had read my rhythm, learned my tricks, and mirrored my decisions. It had been more than prey.

I turned slowly in the current, studying the dead around me. Their eyes still caught light. They looked peaceful in death, as if their last movement had been one of grace. The water carried them in slow circles, small echoes of the pattern that had once defined them.

I realised that I had learned more from this fight than from any before. Not because it was harder, but because it had required thought. The sea did not reward strength forever. The creatures that survived here were the ones that adapted, that read the rules and changed them when they stopped working.

Rules. Patterns. That was the language of survival.

I repeated the phrase in my mind until it settled. It felt like understanding, like the moment before speech becomes meaning.

The System flickered to life in the water before me.

[Environmental Utilisation +1.2%]

The text lingered, bright and cold, then faded into nothing.

I drifted upward, letting the current cool my fins. The plankton fog thinned as I rose. The light from the vent fell away behind me, leaving only the soft shimmer of residual heat. My stomach was full again, but the satisfaction was dull. The fight had taught me something that food could not. The sea was a machine made of rules, and every creature inside it was part of the pattern. To live was to learn the rhythm faster than anything else.

I turned toward the flow and let it carry me. The warmth that had filled the basin began to fade, replaced by the slower chill of open water. The edges of the current wavered and bled into cooler lanes. The shimmer dulled to shadow.

The warmer drift thinned, its heat bleeding into cooler lanes. When the water lost its shimmer, I turned back toward the part of the vent fields I once called home.