maybe dis?

code/modules/events/carp_migration.dm

@@ -2,6 +2,10 @@
 	announceWhen	= 50
 	endWhen 		= 900
 
+	var/list/spawned_mobs = list(
+    /mob/living/simple_animal/hostile/carp = 95,
+    /mob/living/simple_animal/hostile/carp/megacarp = 5,
+	)
 	var/list/spawned_carp = list()
 
 /datum/event/carp_migration/setup()
@@ -17,6 +21,7 @@
 	event_announcement.Announce(announcement, "Lifesign Alert")
 
 /datum/event/carp_migration/start()
+
 	if(severity == EVENT_LEVEL_MAJOR)
 		spawn_fish(landmarks_list.len)
 	else if(severity == EVENT_LEVEL_MODERATE)
@@ -32,14 +37,12 @@
 			spawn_locations.Add(C.loc)
 	spawn_locations = shuffle(spawn_locations)
 	num_groups = min(num_groups, spawn_locations.len)
-	
+
 	var/i = 1
 	while(i <= num_groups)
 		var/group_size = rand(group_size_min, group_size_max)
 		for(var/j = 1, j <= group_size, j++)
-			var/carptype = /mob/living/simple_animal/hostile/carp
-			if(prob(5))
-				carptype = /mob/living/simple_animal/hostile/carp/megacarp
+			var/carptype = pickweight(spawned_mobs)
 			spawned_carp.Add(new carptype(spawn_locations[i]))
 		i++
 

code/modules/events/event_container.dm

@@ -140,7 +140,7 @@ var/list/event_last_fired = list()
 		new /datum/event_meta(EVENT_LEVEL_MUNDANE, "Sentience",			/datum/event/sentience,			50),
 		new /datum/event_meta(EVENT_LEVEL_MUNDANE, "Wallrot",			/datum/event/wallrot, 			0,		list(ASSIGNMENT_ENGINEER = 30, ASSIGNMENT_GARDENER = 50)),
 		new /datum/event_meta(EVENT_LEVEL_MUNDANE, "Aurora Caelus",		/datum/event/aurora_caelus,		15,		is_one_shot = TRUE),
-		new /datum/event_meta(EVENT_LEVEL_MUNDANE, "Koi School",		/datum/event/koi_migration,		80,)
+		new /datum/event_meta(EVENT_LEVEL_MUNDANE, "Koi School",		/datum/event/carp_migration/koi,		80,)
 	)
 
 /datum/event_container/moderate

code/modules/events/koi_mirgration.dm

@@ -1,20 +1,14 @@
-/datum/event/koi_migration
-	announceWhen	= 50
-	endWhen 		= 900
+/datum/event/carp_migration
+	spawned_mobs = list(
+    /mob/living/simple_animal/hostile/retaliate/carp/koi = 95,
+    /mob/living/simple_animal/hostile/retaliate/carp/koi/honk = 2,
+	)
 
-	var/list/spawned_koi = list()
 
-/datum/event/koi_migration/setup()
-	announceWhen = rand(40, 60)
-	endWhen = rand(600,1200)
-
-/datum/event/koi_migration/announce()
-	event_announcement.Announce("Unknown biological entities have been detected near [station_name()], please stand-by.", "Lifesign Alert")
-
-/datum/event/koi_migration/start()
+/datum/event/carp_migration/koi/start()
 	spawn_fish(landmarks_list.len)
 
-/datum/event/koi_migration/proc/spawn_fish(var/num_groups, var/group_size_min=3, var/group_size_max=5)
+/datum/event/carp_migration/koi/spawn_fish(var/num_groups, var/group_size_min=3, var/group_size_max=5)
 	var/list/spawn_locations = list()
 
 	for(var/obj/effect/landmark/C in landmarks_list)
@@ -27,12 +21,12 @@
 	while(i <= num_groups)
 		var/group_size = rand(group_size_min, group_size_max)
 		for(var/j = 1, j <= group_size, j++)
-			var/mob/living/simple_animal/hostile/retaliate/carp/koi/K = new(spawn_locations[i])
-			spawned_koi.Add(K)
+			var/carptype = pickweight(spawned_mobs)
+			spawned_carp.Add(new carptype(spawn_locations[i]))
 		i++
 
-/datum/event/koi_migration/end()
-	for(var/mob/living/simple_animal/hostile/retaliate/carp/koi/C in spawned_koi)
+/datum/event/carp_migration/koi/end()
+	for(var/mob/living/simple_animal/hostile/retaliate/carp/koi/C in spawned_carp)
 		if(!C.stat)
 			var/turf/T = get_turf(C)
 			if(istype(T, /turf/space))

code/modules/mob/living/simple_animal/hostile/retaliate/fish.dm

@@ -53,12 +53,15 @@
 /mob/living/simple_animal/hostile/retaliate/carp/koi/New()
 	..()
 	var/koinum = rand(1, 4)
-	if(prob(1))
-		koinum = 5
 	icon_state = "koi[koinum]"
 	icon_living = "koi[koinum]"
 	icon_dead = "koi[koinum]-dead"
 
 
 /mob/living/simple_animal/hostile/retaliate/carp/koi/Process_Spacemove(var/movement_dir)
-	return TRUE
+	return TRUE
+
+/mob/living/simple_animal/hostile/retaliate/carp/koi/honk
+	icon_state = "koi5"
+	icon_living = "koi5"
+	icon_dead = "koi5-dead"