Spawning left to right

Question

Fishes are supposed to spawn from left to right. And also it seems to be something weird with spawning. Some fishes appear after 20 seconds even if I set up minimum and maximum time of spawning. Also I have doubts about the function add_fish() I'm not sure this is the right way to generate the fishes: 6 kind of fishes and all with the same chance to be generated. What am I doing wrong?

class SpawnTime():
    def __init__(self, previous, time):
        self.time_previous = previous
        self.time = time


class Fish():
    count = 0

    def __init__(self, txr, value, speed):
        self.txr = txr
        self.value = value
        self.speed = speed
        self.x = SCREEN_WIDTH
        self.y = random.randint(0, SCREEN_HEIGHT - self.txr.get_height())
        self.rect = pygame.Rect(
            self.x, self.y, self.txr.get_width(), self.txr.get_height())
        self.is_active = True
        Fish.count += 1

    def draw(self):
        SCREEN.blit(self.txr, self.rect)

    def update(self):
        self.rect.x += self.speed

        if self.rect.right <= 0:
            self.is_active = False


class Player():
    def __init__(self):
        self.txr = PLAYER_TXR
        self.x = 0
        self.y = 0
        self.width = self.txr.get_width()
        self.height = self.txr.get_height()
        self.rect = pygame.Rect(self.x, self.y, self.width, self.height)
        self.score = 0
        self.reset()

    def draw(self):
        SCREEN.blit(self.txr, self.rect)

    def update(self):
        self.x, self.y = pygame.mouse.get_pos()
        self.rect.x = self.x
        self.rect.y = self.y

    def reset(self):
        self.x = self.width
        self.y = SCREEN_HEIGHT//2
        self.rect = pygame.Rect(self.x, self.y, self.width, self.height)
        self.score = 0

    def clicked(self):
        for f in fish_list:
            if f.rect.collidepoint(self.x, self.y):
                self.score += f.value
                f.is_active = False
                SOUND_SLIP.play()
                break  # exit the for loop



def update():
    if playing:
        clock.tick(FPS)

    if playing and not game_over:

        game_time = pygame.time.get_ticks()

        if Fish.count < MAX_FISHES:
            if game_time - fish_spawn.time_previous >= fish_spawn.time:
                fish_spawn.time_previous = game_time
                fish_spawn.time = random.randint(
                    MIN_FISH_SPAWN_TIME, MAX_FISH_SPAWN_TIME) 

                add_fish()

        player.update()

        for fish in fish_list:
            fish.update()

        for fish in fish_list:
            if not fish.is_active:
                fish_list.remove(fish)


def draw():
    SCREEN.blit(TITLE_SCREEN, (0, 0))

    if not playing and game_over:

        if new_high_score:
            draw_text_centred_x(
                f'New High Score: {high_score}', FONT_20,  250, TEAL)
        else:
            draw_text_centred_x(
                f'High Score: {high_score}', FONT_20,  50, TEAL)
            draw_text_centred_x(
                f'SCORE: {player.score}', FONT_30, 170, TEAL)
            draw_text_centred_x('Press SPACE to Play',
                                FONT_30,  350, DARK_GREEN)

    if not playing and not game_over:

        draw_text_centred_x('Press SPACE to Play',
                            FONT_40,  250, DARK_GREEN)

    if playing and not game_over:

        draw_text(f'Score: {player.score}    High Score: {high_score}',
                  FONT_20,  5, 5, DARK_GREEN)


        for fish in fish_list:
            fish.draw()

        player.draw()

def draw_text_centred_x(text, font, y, colour):
    img = font.render(text, True, colour)
    x = SCREEN_WIDTH//2 - img.get_width()//2
    SCREEN.blit(img, (x, y))


def draw_text(text, font, x, y, colour):
    img = font.render(text, True, colour)
    SCREEN.blit(img, (x, y))


def reset_game():

    fish_list.clear()

    player.reset()


def add_fish():

    if random.randint(1, 6) == 1:
        rand = random.randint(0, len(FISHES_TXR)-1)
        txr = FISHES_TXR[rand]
        value = rand+1
        speed = rand*5

        if txr == FISHES_TXR[5]:
            value = -3
      
        f = Fish(txr, value, speed)
        fish_list.append(f)



if __name__ == "__main__":

    playing = False
    game_over = False

    high_score = 0
    new_high_score = False

    player = Player()
    fish = Fish

    fish_list = []

    fish_spawn = SpawnTime(0, MAX_FISH_SPAWN_TIME) 

    # main game loop
    while True:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:  
                quit()
            elif event.type == pygame.KEYDOWN:
                if event.key == pygame.K_ESCAPE:  
                    quit()
                if event.key == pygame.K_SPACE and not game_over:
                    fish_spawn.time = MAX_FISH_SPAWN_TIME
                    playing = True
                    

                if event.key == pygame.K_SPACE and not playing:
                    # new game
                    playing = True
                    game_over = False
                    new_high_score = False
                    player.score = 0

                    fish_spawn.time = 700
                    Fish.count = 0

                    pygame.time.delay(500)  # pause for 500ms = 0.5s

            elif event.type == pygame.MOUSEBUTTONDOWN:
                player.clicked()

        if playing:
            update()
            if Fish.count >= MAX_FISHES and len(fish_list) == 0:
                game_over = True
                playing = False
                if player.score > high_score:
                    new_high_score = True
                    high_score = player.score

                draw()

                pygame.time.delay(500)  # pause for 500ms = 0.5s

        draw()

        pygame.display.update()
        clock.tick(FPS)
    
    pygame.quit()