Environmental Health 3 - Foods & Feeding
In this article ANDY HORTON examines the feeding cycle in the seas, and discusses some of the edible molluscs and crustaceans found on the shore, and foods available from aquatic shops that are suitable for British sea life kept in aquaria. The basic principles are applicable to the tropical reefs.
Big fish eat little fish. This is a grossly simplified view of the undersea jungle. An understanding of the dynamics of the marine food chain provides some guide to keeping the fish and invertebrates alive in the aquarium. In this generalised diagram of the organic cycle of the sea, we can see that the presence of one group of creatures provides sustenance for more complex animals.
DIAGRAM OF THE ORGANIC CYCLE to be posted at a later date in 1999.
Real seawater contains phytoplankton, invisible microalgae, single-celled organisms, principally diatoms and flagellates. Phytoplankton provides the food for filter-feeders like the Sea-Mats (Bryozoa), Sea-Squirts (Tunicates), and bivalve molluscs such as mussels and oysters. It is eaten by the zooplankton, comprising 90% of very small crustaceans, and includes the eggs and larvae of fish and invertebrates. If you follow the cycle round, you will find that the Zooplankton is consumed by other invertebrates including the Hydroids and Sea Anemones (Anthozoa), and Crustaceans. Zooplankton is a vital part of the fry and juvenile fish of all species, and the adults of Pipefish and the Sea Horses. All, in turn, are predated upon by larger animals.
Dead animals and decaying organic waste is scavenged by specially
adapted creatures; the whelks, worms and some of the crabs. Even detritus
is eaten by the lugworm and certain Cushion Stars
like Porania pulvillus, found offshore in Scottish waters. Ammonia
is expelled directly by the fish and other animals, and is also released
during the decomposition of dead organisms. The final stage is acted upon
by bacteria in the 'Nitrogen Cycle', leaving nutrients which are used in
the creation of algae, the phytoplankton and larger seaweeds. There are
other waste products of which the most important is the Carbon Dioxide
respired by all living creatures, including bacteria; and is essential
in the photosynthesis process.
Most of the species kept are predators an scavengers, often ubiquitous feeders. They will eat everything meaty presented to them. I prefer to feed the various fish and invertebrates what they would eat in the wild. There are two principal reasons. Firstly, their chances to thrive in a healthy condition are improved if they are fed on natural live food. Secondly, one of the major fascinations of keeping British marine life in aquaria, is what can be termed the 'ecology of behaviour' of the varying creatures. As feeding is one of the principal activities, it is interesting to watch how the different fish and invertebrates deal with items of prey. The aggressive Shore Crab, Carcinus maenus, has a particularly varied diet. On the shore, it is frequently found with a polycheate worm in its claws. In aquaria, it demonstrates its ability to tackle mussels and cockles, shrimps (Crangon), univalve (snail-like) molluscs, Hermit and other small crabs. It is generally regarded as undesirable because large crabs will prey upon the more delicate animals. Fish like the Common Blenny, Lipophrys pholis, possess sharp comb-like teeth that enables them to crunch barnacles from rocks and attack hard-shelled crustaceans.
Shore collectors will have access to a range of molluscs, worms and crustaceans found in the littoral zone. Tropical aquarists are warned against using most of these foods because of the likelihood of introducing disease organisms. Parasites occur as free-swimming animals. Anemones contain seawater and could be responsible for introducing pathogens into the tank. Gamma-irradicated frozen natural foods from aquarist shops, provide a useful alternative diet.
My observations on British rock pool fish indicate that parasites
are regularly present. Pragmatically, the most sensible procedure is to
ensure healthy conditions in the aquarium. Most parasites only become unsightly,
and a danger to the fish if it is already weakened by poor husbandry.
Fish and other animals require a diet comprised of proteins, carbohydrates,
fats, vitamins and minerals. British shore species are carniverously inclined,
and providing the essential amino acids means that a large part of the
diet must consist of fishy foods found in their natural environment, or
substitute food providing similar ingredients. Wild food can be collected
on visits to the coast.
NATURAL FOODSTUFFS FROM THE SHORE
MUSSEL Mytelis edulis
Mussels reproduce in spring and afterwards become depleted of flesh. The small female Pea Crab, Pinnotheres sp. often resides inside. Cemented to the outside are Acorn Barnacles which provide equally attractive food. Whole mussels (up to 6) can be kept alive for a few weeks in aquaria and will provide natural food for the Common Starfish, Asteria rubens, and the Dog Whelk, NucelLapillus. There are at least 8 species of mussel found in British seas, including the Horse Mussel, or Clabachdubh, Modiolus modiolus.
EDIBLE COCKLE Cerastoderma edule
Cockles can be found buried just below the surface of the sand. They can be prised open by inserting a knife in between the two halves of the shell, and fed raw to the fish and crabs. They will survive for over one month in aquaria. There are numerous other sand burrowing bivalves, Carpet shells, and Tellins found on British shores.
LIMPET Patella vulgata
Limpet and 'scars' on the sandstone at Cullercoats, Tyneside.
Limpets have tough flesh and are best fed after they have been boiled for over 5 minutes. Relished by Wrasse, but all fish prefer a mussel diet.
elegans and P.serratus.
Visitors are frequently fascinated by their complex behaviour and feeding habits. Small prawns will be immediately attacked and killed by Wrasse (Labridae), and swallowed whole by young Bass. The Bullhead, Taurulus bubalis, will ambush this crustacean, and diminish a population kept in the same aquarium. Only newly moulted prawns fall victim to Beadlet Anemones.
Live prawns are the second most important natural food. Many aquarists keep a spare tank to ensure a supply throughout the Winter, when they are found in deeper water offshore. Freshly killed prawn is sometimes accepted by difficult species that refuse Mussel.
OTHER SMALL CRUSTACEANS
SHORE CRAB Carcinus maenas
RAGWORM Nereis diversicolor
Other worms can be tried. Detritus feeders like the Lugworm, Arenicola marina, tend to foul the water and are best avoided.
PERIWINKLES Littorina littorina
Live winkles may be responsible for the introduction of the parasite
lingua which encyst to form black blisters on shore fish such as
the Butterfish and the Rocklings.
BRINE SHRIMP EGGS
Many filter-feeders consume exclusively phytoplankton and keeping them alive can be difficult. Hatchery researchers have fed the larvae of Oyster on cultures of minute green flagellates and diatoms. Marine Rotifer cultures are now becoming available through specialist aquarium retailers.
ADULT BRINE SHRIMPS (LIVE)
MARINE FLAKED FOOD/DRIED FOODS
by Andy Horton 1980s