Myxobolus aeglefini in Wittlingen (Merlangius merlangus)der Nordsee und der lrischen See

In June 1994 and 1995 stations in the North, Irish, Celtic Seas and the Channel were studied for the occurrence of Myxobolus aeglefini in whiting (Merlangius merlangus). The disease was visible externally as either white nodules of a few millimeters diameter in the upper mouth cavity, gill arches and the basis of pelvic fins and in severe cases also on the lower jaws or in the cornea and sclera of the eye. It was verified morphometrically in histological sections of infected eyes by size and shape of spores. Myxobolus aeglefini was present in low prevalences at two North Sea stations and high prevalences of up to 49 % in the Irish Sea (Solway Firth) during both cruises. Whiting between 23 and 55 cm were found to be infected. Neither length-age prevalences nor condition factors and gonado, spleen, liver somatic indices differed in diseased and healthy fishes.

Development and growth of hatchery-reared larval Florida pompano (Trachinotus carolinus)

Although the Florida pompano (Trachinotus carolinus) is a prime candidate for aquaculture, the problematic production of juveniles remains a major impediment to commercial culture of this species. In order to improve the understanding of larval development and to refine hatchery production techniques, this study was conducted to characterize development and growth of Florida pompano from hatching through metamorphosis by using digital photography and image analysis. Newly hatched larvae were transparent and had a large, elongate yolk sac and single oil globule. The lower and upper jaws as well as the digestive tract were not fully developed at hatching. Rotifers were observed in the stomach of larvae at three days after hatching (DAH), and Artemia spp. were observed in the stomach of larvae at 14 DAH. Growth rates calculated from total length measurements were 0.22 ±0.04, 0.23 ±0.12, and 0.35 ±0.09 mm/d for each of the larval rearing trials. The mouth gape of larvae was 0.266 ±0.075 mm at first feeding and increased with a growth rate of 0.13 ± 0.04 mm/d. Predicted values for optimal prey sizes ranged from 80 to 130 μm at 3 DAH, 160 to 267 μm at 5 DAH, and 454 to 757 μm at 10 DAH. Based on the findings of this study, a refined feeding regime was developed to provide stage- and size-specific guidelines for feeding Florida pompano larvae reared under hatchery con

Snail control by fish: an explanation for its failure

Systematic studies on the performance of fish as snail eaters in waterbodies are rare. Here, trials with a promising African cichlid (Astatoreochromis alluaudi) revealed that the fish were only successful at reducing snail populations if there was nothing better to eat - and this is hardly the case. The fish need solid jaws to crush the snails but do not develop such jaws if they can find other, preferables foods. The prospects for this form of control are also discussed in the broader context.

Traditional and geometric morphometrics detect morphological variation of lower pharyngeal jaw inCoris julis(Teleostei, Labridae)

In the present study, variation in the morphology of the lower pharyngeal element between two Sicilian populations of the rainbow wrasse Coris julis has been explored by the means of traditional morphometrics for size and geometric morphometrics for shape. Despite close geographical distance and probable high genetic flow between the populations, statistically significant differences have been found both for size and shape. In fact, one population shows a larger lower pharyngeal element that has a larger central tooth. Compared to the other population, this population also has medially enlarged lower pharyngeal jaws with a more pronounced convexity of the medial-posterior margin. The results are discussed in the light of a possible more pronounced durophagy of this population.

Food habits of Sowerby's beaked whales (Mesoplodon bidens) taken in the pelagic drift gillnet fishery of the western North Atlantic

We describe the food habits of the Sowerby’s beaked whale (Mesoplodon bidens) from observations of 10 individuals taken as bycatch in the pelagic drift gillnet fishery for Swordfish (Xiphias gladius) in the western North Atlantic and 1 stranded individual from Kennebunk, Maine. The stomachs of 8 bycaught whales were intact and contained prey. The diet of these 8 whales was dominated by meso- and benthopelagic fishes that composed 98.5% of the prey items found in their stomachs and cephalopods that accounted for only 1.5% of the number of prey. Otoliths and jaws representing at least 31 fish taxa from 15 families were present in the stomach contents. Fishes, primarily from the families Moridae (37.9% of prey), Myctophidae (22.9%), Macrouridae (11.2%), and Phycidae (7.2%), were present in all 8 stomachs. Most prey were from 5 fish taxa: Shortbeard Codling (Laemonema barbatulum) accounted for 35.3% of otoliths, Cocco’s Lanternfish (Lobianchia gemellarii) contributed 12.9%, Marlin-spike (Nezumia bairdii) composed 10.8%, lanternfishes (Lampanyctus spp.) accounted for 8.4%; and Longfin Hake (Phycis chesteri) contributed 6.7%. The mean number of otoliths per stomach was 1196 (range: 327–3452). Most of the fish prey found in the stomachs was quite small, ranging in length from 4.0 to 27.7 cm. We conclude that the Sowerby’s beaked whales that we examined in this study fed on large numbers of relatively small meso- and benthopelagic fishes that are abundant along the slope and shelf break of the western North Atlantic.

Predatory behaviour of a perch, Nandus nandus (Ham.)

Predatory behaviour of Nandus nandus was studied by offering Cyprinus carpio as prey. The study was conducted with six N. namdus (8.2 ±0.2 cm and 7.60 ±0.3g) represented as P 1, P 2, P 3, P 4, P 5 and P 6. Three size categories of prey (C. carpio) such as small (2.0 ±0.1 cm and 0.23 ±0.01g), large (3.6 ±0.1 cm and 0.57 ±O.O.lg) and mixed group consisting of both small and large prey were used for 14 days of trial. Predatory behavior was classified as targeting, driving, catching, handling, resting and next attempt of catching prey. After introduction of prey into the aquarium predators followed the movement of preys by eye movements and tried to target smaller one first. The predator grasped the head of the prey by its jaws by a drive and engulfed it wholly into the mouth. The average handling time (time taken to manipulate and swallow prey from capture to ceasation of pharyngeal movement) was 42±2 sec and 47±2 sec for small and large prey respectively. N. nandus were ingested more small prey than large prey though the size classes were equally available in case of mixed prey used. Although the prey consumption was higher in number when small prey were ingested but in weight the consumption was higher when ingested large size of prey. The study indicated that N. nandus, ingested more small prey and grasped the headfirst.

Genetic status of selected fish taxa in relation to conservation of genetic and species diversity in the Victoria and Kyoga Lake basins

Cichlids are known for their explosive radiation especially in the African Great Lakes marked with a high level of lake endemism. These fishes have been characterized mainly along trophic and habitat differences, by variation in morphological structures such as teeth and jaws and by differences in body shape and coloration. Cichlids are important as a microcosm of macroevolution. The explosive radiation, young evolutionary scale, and the isolation of groups characterized with high levels of endemism and presence of living fossils makes the group important for evolutionary and genetic studies. Lake Victoria region cichlids which are isolated and relatively more recent in evolution were the last to be appreciated in their diversity. Recently Ole Seehausen has found scores of rock fishes in Lake Victoria which were up to then thought to be absent from the Lake and only known to occur in Lakes Malawi and Tanganyika. Greenwood put together the species groups of Lake Victoria, and later in the early 1980's revised the classification of haplochromine species to reflect the phyletic origin and interrelationship of the various groups in Lake Victoria region. Melan Stiassny has been interested in early evolution of cichlids while the likes of Paul Fuerst and Lees Kaufman and Axel Meyer have been interested and are working to explain the speciation mechanisms responsible for the explosive radiation and evolution of cichlids. Locally S.B Wandera and his student Getrude Narnulemo are spearheading the biodiversity and taxonomic studies of cichlids in Lake Victoria region