SynopsisThe wide variety of aquatic food is considered to be instrumental for the diversification in fish species. Yet their abilities and inabilities of handling food are poorly known. For these reasons the food processing and feeding repertoire of the adult carp, Cyprinus carpio, fed on a variety of food types, were analyzed by lightand X-ray cinematography of the head parts and by electromyography of the head and body muscles during feeding. Nine stereotyped movement patterns (particulate intake, gulping, rinsing, spitting, selective retention of food, transport, crushing, grinding and deglutition) compose the feeding process, their sequence and frequency were adjusted to the type of food. Following quantitative morphological analysis at macroscopic, light-and electronmicroscopical level, the relations between the functioning and architecture of the feeding apparatus were established. The structure and dimensions of the mouth opening, the protrusible upper jaw, the slit-shaped pharyngeal cavity, the palatal and postlingual organ, the branchial sieve, the pharyngeal masticatory apparatus and the distribution of taste buds, mucous cells and muscle fibers along the oropharyngeal surface were the directive structural characters used for estimating the abilities in food processing. The specializations for utilizing food items and its limitations, derived from structural and functional data, are compared with diet data found in the literature in order to evaluate the relative position of the carp in competition for food in the aquatic environment. It is established that the 'omnivorous' carp is specialized in effective handling of several categories of aquatic food, even when these are mixed with non-food (bottom invertebrates ~4% SL in diameter) since the palatal organ enables the carp to separate food from non-food. This includes very hard-skinned food items, processed with the powerful pharyngeal jaws of the fish, and to a lesser extent zooplankton (>250pm). The carp is at the same time very limited in processing long and struggling prey (e.g. fish) as well as vegetable matter, due to the lack of oral teeth and the specialized morphology of its pharyngeal chewing apparatus. These feeding abilities agree with diet data from literature. The reported herbivorism of carp illustrates its opportunism in feeding behaviour. Specialization in feeding is discussed and the necessity to take into account the total series of post-capture feeding actions for a more complete view on trophic specialization. Food intake and the intra-oral food processing of carp are bound to the structures of its sensory, central processing and effector apparatus and to the plasticity in their functioning. These together determine its feeding efficiency in exploiting the available aquatic food resources. Next to ethological and ecological studies functional morphology is another important tool to explain the trophic interactions of fish. 162

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In October-December 1990, the large barbs (Barbus) that contribute more than 35% of the catch in lake Tana (northern Ethiopia) were studied. Previous authors (Riippelll837, Boulenger 1902,1911, Bini 1940 described from 6 to 23 (sub)species for the lake. Banister (1973) lumped all of these into one subspecies: Barbus intermedius intermedius Riippell, 1837. We found that the Lake Tana Barbus could be readily categorized in at least 13 discrete morphotypes, some of which were already distinguished by local fishermen. None of the known descriptions are adequate to distinguish the barbs unambiguously, which is important for monitoring and management of developing fisheries. Intermediates between morphotypes were rare (< 10%). By applying canonical discriminant analysis on a set of 17 morphometric characters (including some directly associated with feeding) our initial morphotype-distinction was confirmed. Also, differences between the morphotypes in distribution, related to depth and substratum were found, as well as differences in intestinal contents, a key to the food-niche. The high number of piscivorous morphotypes (8 out of 13) was striking as piscivory is relatively rare among cyprinids. Piscivory was found to be highly correlated with morphological (feeding related) characters. The presence of discrete morphotypes, that also differ in food-niche and distribution, strongly suggests that several distinct populations exist, that may be (partly or completely) reproductively segregated. Knowledge about these populations, that may represent separate units of fish stock, is of crucial importance for the management of sustainable fisheries and protection of the biodiversity in Lake Tana. It is possible that several species or even a unique cyprinid species flock are present, that urgently need protection.

Reproductive segregation among the large barbs Barbus intermedius complex, Cyprinidae, of Lake Tana, Ethiopia, was investigated in the mouths and upstream reaches of rivers tributary to the lake, during the spawning seasons of 1993 and 1994. The percentage of running fish of four Barbus morphotypes [Acute (Ac), Bigmouth big-eye (Be), Intermedius (In), and Shorthead (Sh)] peaks with the highest water level of the lake. Large differences are apparent in the minimum fork length of running fish among morphotypes [c. 12 cm for male Sh and 28 cm for male Bigmouth small-eye (Se)]. Significant differences occur in temporal, but especially in spatial patterns of the relative abundance of running morphotypes, when the lake is compared with the four major river mouths and their upstream reaches. These different relative abundances are clearest among Ac, Be, In, Sh and Troutlike (Tr). Also, the absence from the rivers of some morphotypes that are usually abundant in the lake itself [Barbel (Ba), Dark (Da), Lip (Li), and Zurki (Zu)], and the abundant presence in the rivers of Tr, rare in the lake, strengthen the hypothesis that spatial and/or temporal spawning segregation is present among the morphotypes. There are indications that Bighead (Bh) and Zu spawn in the lake itself, while other morphotypes were only found running in or near rivers. Combined with the morphological, ecological, and genetic differences, these data suggest the existence of several Barbus species, forming a unique species flock, which probably evolved within the lake. The presence of several, instead of one Barbus species complicates management of sustainable fisheries and protection of the lake's biodiversity. Present results show the importance of the rivers for Barbus reproduction and stress the urgent need for careful management of fishing activities in spawning times and areas. 1996 The Fisheries Society of the British Isles

The oropharyngeal feeding mechanism of the carp was analysed as a case study for cyprinids. Light and X‐ray cinematography combined with electromyography allowed a detailed analysis of the external and internal events during processing of the following food types: radtopaque pellets, earthworms, barley, tubificids, cladoceran suspensions and food‐soil mixtures. Ten patterns of head movements serve 12 feeding actions: paniculate feeding and gulping for intake; rinsing, repositioning, selective retention and spitting for selection; gathering from the branchial sieve, transport, loading of the teeth, crushing, grinding and deglutition. Muscular cushions in the pharyngeal roof (palatal organ) and floor (postlingual organ) permit postcapture selection between food and non‐food and transport. Protrusion of the upper jaw is crucial in food processing and serves different aims in particulate intake, gulping and internal selection. The mechanism of each single pattern and its effects in manipulating the flow and particles is discussed. Restrictions for processing different types of food are formulated. Tentative limits are set to the feeding on the available food types in the environment. The feeding apparatus appears to be unsuitable for exploiting very small particles (< 250 μm), plant and other materials of fibrous content. Only slow and immobile food particles with a diameter up to c. 4% of the carp's body length are effectively processed. The carp appears to be a generalist in its diet, with specializations for the exploitation of food and non‐food mixtures from the bottom, even if the contained food is of considerable density and hardness. The distinct elements of feeding behaviour are considered to be stereotyped action patterns. They are released and steered according to the actual size, distribution, consistency and contamination of the food and integrated into varied probing and feeding sequences. Different food types require different movement patterns and ‘handling times’. Protrusion with closed mouth appears to be a core pattern in food handling as it is basic to several feeding actions (repositioning and back‐washing during purification; gathering of retained food from the branchial sieve). Protrusion and the palatal and postlingual organs in this lower teleost are basic to the substrate feeding habits of many cyprinoids and are discussed in relation to (i) the hypertrophy of the pharyngeal masticatory apparatus, (ii) the recruitment of body power for mastication, and (iii) the evolutionary loss of toothed upper pharyngeal transporting bones. A scheme connects the unique character set of cypriniform fish to the origin and evolution of their feeding mechanism. The cooperation between functional morphology, ethology and ecology for the study of niche separation between species is emphasized.