The distribution and function of mucous cells and their secretions in the alimentary tract of Arrhamphus sclerolepis krefftii

The mucosa of the mouth, pharynx, oesophagus and rectum of Arrhamphus sclerolepis krefftii contain saccular mucous cells and the lining of the intestinal mucosa contains goblet mucous cells. Saccular mucous cells in the buccal epithelium are present in relatively low densities and contain acidic and neutral glycoprotein-secreting cells in an approximately 1:1 ratio. The saccular mucous cells in the mucosa of the pharynx, oesophagus and rectum are abundant and contain acidic glycoprotein which consists principally of sialomucin with traces of sulphomucin distributed around the periphery of the mucous vacuoles. Goblet cells in the intestinal mucosa contain neutral glycoprotein. Mechanically digested plant material within the lumen of the gut is bound by a sheath of acidic glycoprotein which is in contact with the intestinal mucosa. From these observations and with information on the known properties of acidic glycoproteins, a novel mechanism for the involvement of mucus in the extraction of nutrients from plant material mechanically digested by fish is proposed.     

Shaping of the lower jaw bone during growth of Nile tilapia Oreochromis niloticus and a Lake Victoria cichlid Haplochromis chilotes: a geometric morphometric approach

East African cichlids have evolved feeding apparatus morphologies to adapt to diverse feeding environments. However, little is known about how the morphologies are formed during development. Here, we assessed the shape changes of the lower jaw bone during growth of the Nile tilapia Oreochromis niloticus and a Lake Victoria cichlid Haplochromis chilotes using geometric morphometric methods. 'Early Juvenile to Late Juvenile' and 'Late Juvenile to Adult' transitions of the shape change during growth of both O. niloticus and H. chilotes were detected. The 'Early Juvenile to Late Juvenile' transition of the shape change in H. chilotes occurred slightly earlier than in O. niloticus. We also compared the shape changes during growth of the two cichlids. Principal component analysis showed both commonalities and differences in the morphological changes between the cichlids. Our data suggest that most shape change may have a similar pattern during the growth of O. niloticus and H. chilotes, and that the differences in adult shapes may be due to differences arising early in development, not to the difference of shape change during growth. These data provide a basis for understanding the developmental mechanisms underlying this adaptive trait of East African cichlids.     

Relationship between gape size and feeding selectivity of fish larvae from a Neotropical reservoir

Larvae feeding selectivity of Iheringichthys labrosus , Hypophthalmus edentatus and Plagioscion squamosissimus was assessed, examining the role of mouth gape in prey selection. Fish larvae were sampled in the Itaipu Reservoir (Brazil–Paraguay). Iheringichthys labrosus and H. edentatus larvae, with small and similar gape sizes, exhibited slightly different diets; I. labrosus preferred cladocerans ( Bosmina hagmanni , Bosmina huauriensis and Bosminopsis deitersi ) and the rotifer Brachionus calyciflorus . Hypophthalmus edentatus , however, primarily ingested the cladocerans B. hagmanni , Ceriodaphnia cornuta , Daphnia gessneri and Diaphanosoma spinulosum . Plagioscion squamosissimus , with a greater gape size, preferred Calanoida. The mechanistic processes that determine food selectivity of fish larvae in temperate aquatic systems were similar in the Neotropical system. The trophic spectrum of these species is characterized by small- to intermediate-sized prey. Plagioscion squamosissimus larvae, which have larger mouths, exploit primarily larger prey differing from the most abundant species or size classes; consequently, their diet is quite different from I. labrosus larvae and modestly similar to H. edentatus larvae, opportunistic feeders that they eat more abundant prey.     

The functional significance of inherited differences in feeding morphology in a sympatric polymorphic population of Arctic charr

Artificially fertilised eggs from wild-caught Arctic charr parents of two sympatric morphs (benthivorous and planktivorous) from Loch Rannoch, Scotland were reared in the laboratory under identical conditions. During the subsequent 2 years, aspects of their trophic anatomy and feeding behaviour were compared. As previously described for wild-caught fish, charr derived from the benthivorous morph had an increasingly wider mouth gape for a given body length than those derived from the planktivorous morph. The functional significance of these differences in gape was tested by comparing the maximum size of prey that could be handled by each of the two morphs. In both forms, a larger gape enabled larger food particles to be eaten, but the elevation of the regression of maximum prey size on gape was higher in the benthivorous form, indicating the existence of additional morphological and/or behavioural differences influencing the size of prey consumed. When offered a choice between a typical benthic prey item and a typical pelagic food item, charr of benthivorous origin were more likely to feed on the former, whereas those of planktivorous origin were more likely to feed on the latter. Thus inherited differences in gape place constraints on foraging ability and are associated with inherited differences in dietary preference. We conclude that the functional significance of the foraging specialisations indicate a strong selection pressure for the evolution of the divergence and propose that heterochronic growth is the mechanism resulting in the divergence of tropic anatomy.     

Phylogeny of Dicranophoridae (Rotifera: Monogononta) – a maximum parsimony analysis based on morphological characters

This study presents the first phylogenetic analysis of Dicranophoridae (Rotifera: Monogononta), a species rich rotifer family of about 230 species currently recognized. It is based on a maximum parsimony analysis including 77 selected ingroup and three outgroup taxa and a total of 59 phylogenetically informative morphological characters. Character coding is based on personal investigation of material collected by the authors and an extensive survey of the literature. Apart from covering general body organization, character coding primarily relies on scanning electron microscopic preparations of the mastax jaw elements. Our study suggests monophyly of Dicranophoridae with a clade of Dicranophorus and Dorria as the sister taxon of all other dicranophorid species. Monophyly of Encentrum , the most species rich genus within Dicranophoridae, cannot be demonstrated. Within Dicranophoridae our study identifies the monophyletic taxa Caudosubbasifenestrata, Intramalleata, Praeuncinata and Proventriculata, each based on unambiguous character transformations evolved in their stem lineages. However, resolution within Praeuncinata and Proventriculata is very limited. Although some terminal clades within Praeuncinata and Proventriculata are recognized, basal splits remain obscure. Probably, other characters such as DNA sequence data are needed to further our understanding of phylogenetic relationships within these poorly resolved taxa.     

Spectacular morphological novelty in a miniature cyprinid fish,Danionella dracula n. sp.

Danionella dracula is a new species of sexually dimorphic, miniature and highly developmentally truncated cyprinid fish. Compared with its close relative, the zebrafish Danio rerio, it lacks 44 bones or parts thereof and represents one of the most developmentally truncated vertebrates. Absence of the majority of bones appears to be due to developmental truncation via terminal deletion. In contrast to these larval-like features, D. dracula also shows several hyperossifications. Uniquely, among carp-like fishes, male D. dracula have a series of long, pointed odontoid processes on the jaws greatly resembling the jaw dentition of teleosts with true teeth. The anterior-most process in each jaw is extended as a canine-like fang projecting through the epithelium. True jaw teeth are absent from all 3700 species of cypriniforms and were lost at least in the Upper Eocene. It remains to be investigated, however, whether the conserved pathways to regulate tooth development in cypriniforms have been used in D. dracula to form and pattern the odontoid processes. This new species represents a remarkable example linking progenetic paedomorphosis via heterochronic change in developmental timing to the evolution of morphological novelties.     

Optimization of foraging and diet by the piscivorous Othos dentex (Serranidae)

The aim of this study was to determine the dietary characteristics and mouth morphology of Othos dentex and to use these data, together with in situ observations of feeding behaviour, to elucidate how foraging and diet are optimized by this piscivorous serranid. Seasonal spear and line fishing over reefs in south‐western Australia yielded 426 O. dentex (total length, L_T, 183–605 mm), among which the stomachs of 95 contained food. The food in the stomachs of 76 fish was sufficiently undigested to be seen to contain, almost invariably, a single fish prey, which was typically identifiable to family and often to species. The prey of O. dentex, which were measured (L_T), represented 10 families, of which the Labridae and Pempheridae constituted nearly two‐thirds of the prey volume. Two‐way crossed analysis of similarities of volumetric data for stomach contents showed that the dietary compositions of the different length classes of O. dentex in the various seasons were significantly related to length class of prey, but not to prey family, length class within the various prey families or season. Furthermore, an inverse (Q‐mode) analysis, including one‐way analysis of similarities, showed that the patterns in the prey consumed by the different length classes of O. dentex in the various seasons were related more strongly to length class than prey family. The former trend is exemplified in a shade plot, by a marked diagonality of the length classes of prey with increasing predator size. The ingestion of typically a single teleost prey, whose body size increases as that of O. dentex increases, reduces the frequency required for seeking prey, thus saving energy and reducing the potential for intraspecific competition for food. The ability of O. dentex to ingest large prey is facilitated by its possession of a very large gape, prominent recurved teeth, dorsal and independently‐moveable eyes, cryptic colouration and effective ambush behaviour. Othos dentex has thus evolved very cost‐effective mechanisms for optimizing its foraging and diet.     

Oxygen minimum zone: An important oceanographic habitat for deep‐diving northern elephant seals,Mirounga angustirostris

Little is known about the foraging behavior of top predators in the deep mesopelagic ocean. Elephant seals dive to the deep biota‐poor oxygen minimum zone (OMZ) (>800 m depth) despite high diving costs in terms of energy and time, but how they successfully forage in the OMZ remains largely unknown. Assessment of their feeding rate is the key to understanding their foraging behavior, but this has been challenging. Here, we assessed the feeding rate of 14 female northern elephant seals determined by jaw motion events (JME) and dive cycle time to examine how feeding rates varied with dive depth, particularly in the OMZ. We also obtained video footage from seal‐mounted videos to understand their feeding in the OMZ. While the diel vertical migration pattern was apparent for most depths of the JME, some very deep dives, beyond the normal diel depth ranges, occurred episodically during daylight hours. The midmesopelagic zone was the main foraging zone for all seals. Larger seals tended to show smaller numbers of JME and lower feeding rates than smaller seals during migration, suggesting that larger seals tended to feed on larger prey to satisfy their metabolic needs. Larger seals also dived frequently to the deep OMZ, possibly because of a greater diving ability than smaller seals, suggesting their dependency on food in the deeper depth zones. Video observations showed that seals encountered the rarely reported ragfish (Icosteus aenigmaticus) in the depths of the OMZ, which failed to show an escape response from the seals, suggesting that low oxygen concentrations might reduce prey mobility. Less mobile prey in OMZ would enhance the efficiency of foraging in this zone, especially for large seals that can dive deeper and longer. We suggest that the OMZ plays an important role in structuring the mesopelagic ecosystem and for the survival and evolution of elephant seals.     

MR Proton Relaxivities of Some Ions, Albumin, and Cholesterol Added to Odontogenic Jaw Cysts

The relaxation rates (1 / T ₁ and 1 / T ₂) in cysts have already been analyzed in terms of materials such as albumin, cholesterol, manganese, iron, and copper. However, the relaxivities of these materials have not been determined yet. In this work, five sets containing the ions, albumin, and cholesterol were prepared by addition of increasing concentration of one material to each set. The relaxation times in these sets were measured by MRI, and the relaxation rates were fitted versus concentrations. The slopes of the fits were used as relaxivities. The (r ₁, r ₂) values of manganese, iron, and copper in mM⁻¹ s⁻¹, and those of albumin and cholesterol in (g/dl)⁻¹ s⁻¹ were found to be (32.64, 89.77), (0.31, 1.19), (0.5, 1.479), (0.01, 0.066) and (0.03, 0.458), respectively. The r ₂/r ₁ ratio ranged from 2.75 to 15.27. Manganese is an efficient relaxer, but iron and copper are poor ones. Albumin and cholesterol are efficient relaxers for only T ₂. The contribution of water associated with native manganese of the cystic fluid to T ₁ was 0.268 s⁻¹, whereas those of water associated with native manganese, albumin, cholesterol, and iron to T ₂ were 0.736, 0.185, 0.092, and 0.076 s⁻¹, respectively. The other contributions were much smaller than 0.076 s⁻¹. Manganese is most likely the compound altering T ₁-weighted images between different jaw cysts, whereas manganese and albumin are most likely the compounds altering the T ₂-weighted images. Present data suggest that such alterations may be used to separate jaw cysts from other jaw masses. The high r ₂/r ₁ suggests that T ₂ is a more convenient parameter than T ₁ for diagnostic use. This work is a part of the PhD thesis of U. Nezih Yilmaz supervised by R. Guner.