Разделил программу на несколько файлов. При компиляции получается вот это. Как исправить?

Question

Код ошибки

   In function `AquariumArray::AquariumArray(unsigned int)': AquariumArray.cpp:(.text+0x55):   undefined reference to `Aquarium::Aquarium()'

main.cpp

#include <stdio.h>
#include "AquariumArray.h"
#define COUNT 2
int main()
{
     AquariumArray aq[COUNT];
     return 0;
}

Aquarium.h

 #pragma once
 #include <stdio.h>
 class Aquarium
 {
  private:
      float height;
      float length;
      float width;
      float heightLiquid;
  public:
      Aquarium();
  };

Aquarium.cpp

  #include "Aquarium.h"
Aquarium :: Aquarium()
  {
       this->height = 0;
       this->length = 0;
       this->width = 0;
       this->heightLiquid = 0;
  }

AquariumArray.cpp

   #include "AquariumArray.h"
AquariumArray :: AquariumArray(unsigned length)
   {
       this->array = new Aquarium[length];
   }

AquariumArray.h

  #pragma once
  #include "Aquarium.h"
class AquariumArray
  {
   private:
       Aquarium* array;
       unsigned length;
   public:
       AquariumArray(unsigned length=0);
};