feeding ecology of fishes Flashcards
what are teleost jaws made of
entirely different elements, formed from dermal bone, rather than around the pre-formed cartilage
what are the 4 parts of teleost jaws
- lower jaw (LJ) or Dentary - formed by Meckel’s cartilage entirely surrounded by dermal bone
- palate (PA) - formed by Palato-quadrate replaced by cartilage bone and dermal bone
- Upper jaw now consists of two dermal bone elements: premaxilla (PM) + maxilla (M)
what was the early part of jaw development
Posterior part of maxilla becomes free from the cheek so it can move
- When the mouth is opened, the maxillae (remember, these bones are paired) rotate forward and down, keeping the shape of a tube (very important considering how most teleosts feed – suction feeding)
- Premaxillae and maxillae are the main teeth carriers in primitive bony fish (as well as tongue and inside of mouth), the relationship changes in higher teleosts
- PM is also hinged in species like herring
what adaptations are made to the PM to suit other species
- Gadoids have a cartilage on top of the PM (rostral cartilage) - pushes the PM infront of the body allowing them to protrude their jaw
- Carps, flatfish, dories, anglers have ascending process (hooked shape at the top) on premaxilla – allows extreme jaw protusion (creates less disturbance to other fish – moves less of the body)
3 types of specialised teeth
- plaice teeth = chisel-shaped for slicing bivalve siphons
- Piscivores’ teeth = may be small, or backward pointing, e.g. Lophius and hake have hinged teeth for gripping
- Pharyngeal teeth often for grinding
Oesophagus characteristics
- Distendable, acts as storage
- Lining only produces mucus, no enzymes in mouth pharynx or oesophagus
stomach characteristics
- Usually well-developed in predators, often large, always distendible with muscular walls
- Usually U, J or Y shaped with well-defined pyloric sphincter and releases hydrochloric acid to prevent decay
- Stomachs in herbivorous fish tend to be small or non- existent
- Detritivores such as mullet have just a thickened region of intestine
Intestine characteristics
- Length of intestine is closely related to diet
- Predators have short (<body length) intestines
- Piscivores typically 0.6 times body length
- Herbivores and detritivores (microphagous) up to 20 times body length
what is the Pyloric caecae
- At pyloric end of intestine
- From 1 to >1000
- Increase absorptive surface area
- Elasmobranchs have spiral valve instead, in lower part of intestine – same function (but this reduces the ability of large items to pass through – they tend to stay in the stomach + get regurgitated)
explain digestion
- Food passes from stomach (chyme) into intestine of predators in discreet gobbets rather than a continuous dribble
- Digestion can be protracted, especially in piscivores, with outer layers being excreted while the remainder is still in stomach
6 types of feeding
1.Predators
2. Grazers and browsers
3. Filter feeders
4. Suckers
5. Parasites
6. Symbioses
**not mutually exclusive e.g. mackerel
predator characteristics
- Vast majority of fish
- All elasmobranchs are predatory (except for 13 species of filter feeders)
- Large, terminal mouths with well-developed biting or grasping teeth
- Can divide into 3 categories:
Ambushers
Searchers
Persuers/stalkers
what 3 categories can we divide predators into
Ambushers
Searchers
Persuers/stalkers
ambush predator characteristics
- Rely on prey coming to them
- Often attract with lures
- Often camouflaged
- Encounter rates unpredictable
- Generalists with wide diet
e.g. pike, anglerfish
searcher predators characteristics
- Actively seek prey
- Spend little time pursuing or handling
- Opportunistic
- Generalists with wide diet but often preferred foods
- A protrusible mouth only works if you are stationary or moving very slowly!
e.g. bass, thresher shark
