Fish

Fish

      To discuss the individual species within such a short document would be impossible so we shall be relating characteristics and environment effects they have upon the pond and its inhabitants,but some examples are included to assist the reader.

   Let us first look at the the Salmonidae, these are well known to most people and often sort after for fishing both for sport and the table. As a general rule a simple means of identification of members of this family is the adipose fin. this is a small fleshy fin which is found between the dorsal fin and the tail. Salmonidea are fish that require well oxygenated waters, so are normally restricted to ponds with a good source of water supply which tends to be at a much lower temperature also which helps the content of dissolved oxygen.

    It was important to get the above statement made because it is a common mistake for the enthusiastic pond owner, to stock his pond with members of the Salmonidea family and then suddenly wonder why they have all died. It also also an important statement in so much as you need to match the requirements of the fish to that of the water, this applies also to stock levels something we shall address later.

    Like all animals fish require food to survive and grow, this foods primary source within the pond is from plants. Whether this is direct source or an indirect one coming from invertebrates or even more complex food-chains is dependant on the species and its requirements. Unlike humans fish even those with teeth do not chew there food within the mouth, some have grinding bones set within the oesophagus whilst others such as predators are able to swallow the prey whole were upon entering the enlarged stomach the digestion process begins. Once the food is digested it can be used to provide energy  for movement, the regeneration of damaged cells or for growth. It must be remembered at this point that the fish is very reliant upon water temperature and its metabolism is controlled by this. So at high temperature the rate of metabolism increases and uses up the stocks of energy from the food source quickly whilst the reverse of course happens at low temperatures.

    A fishes rate of growth depends very much on the quality and quantity of food it receives, this combined with other factors within its environment such as water temperature, available space, water quality. All play there part towards how the fish develop, fish though unlike most creatures are able to adapt there growth rate to suit available resources, when good conditions are available they can grow very quickly. But during times of sparse food they can stop growth totally and maintain there static size fish unlike many other creatures continue to grow throughout there lives even after reaching sexual maturity.

Feeding has always been of interest to both the biologist, angler and also the fish keeper. This is when fish portray there greatest ability for learning and also there opportunist nature. Certain feeding patterns vary very little such of those of the predators or filter feeders. Other species though feed on what is the most desirable or available source, the opportunist species will feed one day on the bottom on invertebrates it may find, whilst the next it takes the hatching larvae of species emerging from the water. The next may be totally different again when it will feed on food which has entered the water from an external source such as insects which have fallen in. This shows how fish will feed using the least amount of energy possible and tend to feed from the easiest available source.

We have briefly described some of the attributes of the fish above but how do they effect a pond its food-chain and physical structure.

Different species of course have there own impact upon a pond but they all have one thing in common the production of waste products. Like all living creatures they consume material, convert to energy then excrete excess materials. Being higher in the food-chain there consumption is large. let us look at the highest members the predators. To produce a 10kg (22lb) predator it needs to consume something like 100kg (220lb) of prey fish. these in turn will have consumed 1 tonne of invertebrates, which will in there production have consumed 10 tonne of plant and algae material. From these figures it is possible to see that the impact of one large fish is considerable. All through the fishes life it is of course producing waste products both in the form of excretion and carbon dioxide through respiration. These require conversion by lower members in the food chain and plants so that they can be utilised within the ponds structure.

It was mentioned above that different species have different impacts upon the ponds structure. Therefore it is important if consideration is to be given to stocking a pond as to what species are to be added. If we divide the types of fish in to feeding types and areas it does assist in determining what sort of possible effects they will have. Most fish can be divided into simple groups such as those listed below.

1. Bottom Feeders
2. Mid-water & Bottom Feeders
3. Mid-water & Top Feeders

These can then be divided even further into feeding types, which are again listed below.

1. Herbivore
2. Pelagial Zooplantivor
3. Weed-Bed Zooplanktivor
4. Piscivorous.

You can see from the range of feeding habits and food sources that they cover all available food sources within the pond. Each area of feeding has a different form of impact, bottom feeders are likely to impact the water by causing disturbance of the bottom sediments which will increase turbidity. This in turn will reduce plant growth and impact the production of invertebrates within the pond. Thus reducing available food sources for other species and generally reducing the productivity of the water. An excess of mid-water or top feeders is likely to reduce drastically the invertebrate population, this would lead to stunted fish growth and again a decline in the productivity of the water plus the likelihood of algal blooms as the invertebrate consumers are removed from the system.

So as you can see from the above information the fish within a pond not only act as the top of the pyramid in the food-chain, but can also greatly impact the very structure of the pond itself. So any form of stocking needs to be carefully considered and if possible an insight gained as to the fishes behaviour,optimum growth size and the possible consequences of its addition.