WAU dissertation no. 1010.General Summary
Title: Food handling and
mastication in the carp (Cyprinus carpio L.).
The process of food handling in the common carp (Cyprinus carpio L.) and its structures associated with feeding are analyzed. The aim of this study is to explain the relation between the the architecture of the head and its functions in food processing and to determine the specializations for some food types and the consequent restrictions for others. Such information improves our understanding of the trophic interrelations between different fish species living together in one community.
- Cyprinids possess pharyngeal jaws, which are modified fifth branchial arches. These are moved by the modified branchial arch muscles against a horny chewing pad in the skull. Oral teeth and a stomach are absent. The upper jaws are protrusile and so aid in the formation of a round suction mouth. The oral and opercular cavity are highly variable in volume. The pharynx is almost fully occupied by the dorsal palatal organ. The pharyngeal floor is composed of the postlingual organ and the branchial sieve. Fibre systems of striated muscles form the bulk of these organs. The branchial arches bear numerous gill rakers. The surface of the pharyngeal roof and floor is almost fully covered by taste buds (up to 82 0/MM2 ) and mucous cells. The medullar nervous centre of these organs is of about equal size as the forebrain. The narrow slit-like space between both organs has a restricted capacity for volume change, contrary to the situation in most other fishes.
- The role which these structures perform during food uptake and processing in the carp was investigated using cine- and X-ray filming techniques and by synchronously recording the electromyograms of the involved muscles (9 channels). The morphology was studied on the macroscopical and on light- and electronmicroscopical level. Food types included commercial fish pellets, barley, earthworms, tubifex, cladocerans and tubifex-soil mixtures. BaSO4-impregnated food was used to follow its path in the X-ray movies.
- Each feeding process is composed of a variable number of stereotyped movement patterns, viz: particulate intake and gulping, selection between food and non-food material (through rinsing, repositioning and backwashing), recollection from the branchial sieve followed by food transport and filling of the chewing cavity, crushing, grinding and deglutition. Probing of the soil and spitting are considered separately.
- The timing, amplitude and velocity of mouth opening, protrusion of the upper jaws, opening of the opercular valve and of the volume changes in the oral, buccal, pharyngeal and opercular cavities determine the effects of each single pattern. Food intake, selection, transport and mastication impose different demands on the head and can not be combined effectively.
- Different food types are processed in sequences of movement patterns varying in frequency and type according to the specific size, consistency and soilure of the food. Handling times are read from the electromyograms and may differ widely.
- The quantitative distribution pattern of taste buds, mucous cells, club cells and muscle fibers over the oro-pharyngeal surface is measured. Based on these patterns and on other structural characters six areas are distinguished in the oro-pharynx and related with the functions of the above movement patterns for food intake and processing. Scanning E.M. pictures are presented of the common epithelial cells with microridges, cornified cells, mucous cells, taste buds and sensory (?) oligovillous cells.
- Particulate intake is
accomplished by fast and voluminous suction, caused by expansion
of the orobuccal and opercular cavities. The upper jaws are
protruded to produce a fast suction flow (>60 cm/sec), aimed to
- High densities of club cells, which produce the cyprinid alarming substance in the skin, also occur in the orobuccal lining. Their alarming function in this area is doubted.
- Selection between food and non-food requires the retention of edible particles and the expulsion of waste. The electromyograms and electrical stimulations indicate that this separation is achieved by momentary bulgings on the palatal organ, fixing edible particles between pharyngeal roof and floor. Waste particles are flushed through the branchial slits. The complex structure of the palatal organ, the almost maximal densities of taste buds and the cyto-architecture of its regulatory centre in the hindbrain suggest a high level of discrimination in this selection process. The slit-shaped pharynx guarantees a large contact area for selection, but limits its role in suction.
- Protrusion of the upper jaws with the mouth closed plays a crucial role in selection by resuspending food and non-food in the expanding oral cavity. Alternative expansion and compression of the oral cavity creates a for- and backward flow through the pharyngeal slit and the branchial sieve. Repetition of such 'closed protrusions' and selection effects are graded increasing purification. Closed protrusion movements also serve for merely repositioning of large particles and for recollection of the filtrate from the branchial sieve.
- Cells producing low-viscosity
mucus (sialomucines) are found rostrally in the oro-pharynx. It
probably serves in lowering the resistance of the wall for the
flow of water and in protection of the underlying tissue.
- Transport of food enveloped in mucus is effected by a peristaltic type of movement in the palatal and postlingual organs. These also propel the food into the chewing cavity being enlarged by depression of the pharyngeal jaws.
- The pharyngeal jaws are suspended in muscular slings from the caudal part of the skull and pectoral girdle. Except an antero-ventral gliding joint with the branchial basket no articulations are present. The symphysis of the jaws allows intrinsic movements. Food is crushed and ground between the pharyngeal teeth and a cornified chewing pad, fixed to the base of the skull. Mastication of grains of maize produces distinct sounds, even distinct close to the experimental tank.
- The epaxial muscles of the carp contribute through rotation of the skull high forces to crushing and grinding. The hypaxial muscles transfer their forces to the pharyngeal teeth by retraction of the pectoral girdle, which provides a large moment-arm. The pharyngeal masticatory apparatus is built for producing and resisting high forces.
- Contrary to these 'power muscles', the hypertrophied pharyngeal jaw muscles act more like 'steering muscles'. They direct and stabilize the pharyngeal jaw movements around four anatomical rotational axes.
- The chewing construction with the rotating skull renders a single Weberian ossicle connecting the sound receiving swimming bladder and the internal ear inside the skull almost impossible. The chain of Weberian ossicles running close to the rotation centre of the skull seems to be a constructive necessity.
- Deglutition is accomplished by compression of the chewing cavity. Bulging of the palatal and postlingual organs closes the entrance and thus direct the transport to the esophagus. Movements of the pharyngeal jaws support transport.
- The apparatus for food uptake
and food processing of the carp appears to be specialized to deal
with medium-sized and hard food particles (e.g. seeds and shelled
mollusks), from 250 pm to about 3% of its standard body length,
but also for food items mixed with unedible material. These
specializations for bottomfeeding are most likely basic to the
present wide distribution of the common carp and facilitate fish
- A tentative scheme relates characters from different parts of the head and unique to the cyprinid family in a functional and structural context. The development of the masticatory apparatus may well have been a key adaptation in the origin of the cyprinid feeding mechanism.
- The present research of the carp provides a new and detailed startingpoint for investigation of the regulatory mechanisms in feeding and for comparisons with native cyprinids like bream roach, tench etc. Knowledge of abilities and restrictions of their structural specializations associated with feeding eludidates which plasticity the fish has to utilize different types of food. This plasticity is a crucial factor for the survival of the species in conditions of food scarcity and co-determines its position in competition. The obtained knowledge thus aids in predicting the effects of environmental changes on the trophic interactions and composition of the fish fauna.