aquarium_123

using System;
using System.Collections.Generic;

namespace Aquarium
{
    class Program
    {
        static void Main(string[] args)
        {
            string userInput = null;
            Aquarium aquarium = new Aquarium();

            while (userInput != "4")
            {
                Console.SetCursorPosition(0, 15);
                aquarium.ShowInformation();
                Console.SetCursorPosition(0, 0);
                Console.WriteLine("1 - Do nothing\n2 - Add fish\n3 - Remove fish\n4 - Exit");
                userInput = Console.ReadLine();
                switch (userInput)
                {
                    case "1":
                        break;
                    case "2":
                        aquarium.AddFish();
                        break;
                    case "3":
                        Console.WriteLine("Which fish? (number)");
                        int number = Convert.ToInt32(Console.ReadLine());
                        aquarium.RemoveFish(number);
                        break;
                    case "4":
                        break;
                }
                aquarium.PassOneCycle();
                Console.Clear();
            }
        }
    }

    class Aquarium
    {
        private List<Fish> _fishes = new List<Fish>();

        public int MaxFishes { get; private set; }

        public Aquarium()
        {
            List<Fish> fishes = new List<Fish>();
            MaxFishes = 10;
        }

        public void AddFish()
        {
            if (_fishes.Count <= MaxFishes)
            {
                Fish newFish = new Fish();
                _fishes.Add(newFish);
            }
            else
            {
                Console.WriteLine("The aquarium is full!");
                Console.ReadKey();
            }
        }

        public void RemoveFish(int number)
        {
            if (number - 1 <= _fishes.Count && number > 0)
            {
                _fishes.RemoveAt(number - 1);
            }
        }

        public void PassOneCycle()
        {
            foreach (var fish in _fishes)
            {
                fish.GetOlder();
            }
        }

        public void ShowInformation()
        {
            Console.WriteLine("Список рыб: ");
            int i = 0;
            foreach (var fish in _fishes)
            {
                Console.WriteLine($"[{i + 1}] - Age - {_fishes[i].Age}, Is it alive? - {_fishes[i].isAlive}");
                i++;
            }
        }
    }

    class Fish
    {
        public int Age { get; private set; }
        public bool isAlive { get; private set; }

        public Fish()
        {
            Age = 0;
            isAlive = true;
        }

        public void GetOlder()
        {
            Age += 1;
            if (Age > 10)
            {
                isAlive = false;
            }
        }
    }
}