Micropogonias undulatus(L.), another exotic arrival in European waters

Two living specimens of the Atlantic croaker Micropogonias undulatus have been caught during recent years in Belgian waters (Southern Bight of the North Sea): one in August 1998 as a by‐catch of the commercial shrimp fishery in coastal waters, another in October 2001 on a tidal flat in the brackish part of the Scheldt Estuary. These represent the first records of this north‐west Atlantic species in European waters, and their occurrence is likely to be due to transportation in ship ballast water.     

The use of haematoxylin stain to improve contrast of growth increments in otoliths of larval whitemouth croaker

Otoliths of larval whitemouth croaker Micropogonias furnieri , treated with haematoxylin, exhibited a clearer pattern of incremental and discontinuous zones than untreated otoliths. Precision of age estimates was better after the staining procedure.     

Population dynamics and community analysis of the parasite fauna of juvenile spot, Leiostomus xanthurus (Lacepede), and Atlantic croaker, Micropogonias undulatus (Linnaeus), Sciaenidae) in two estuaries along the middle Atlantic coast of the United States

The parasite communities of juvenile spot, Leiostomus xanthurus Lacepede, and Atlantic croaker, Micropogonias undulatus (Linnaeus), changed with size, season. and geographical area. A total of 21 parasitic species occurred in juvenile spot and 19 occurred in juvenile croaker from Chesapeake Bay and Pamlico Sound. More parasitic species were acquired as juveniles grew, diversified their diets, and consumed larger numbers of intermediate hosts. They were also exposed to infective larvae of parasites with direct lifecycles over long periods of time. Equibility and, thus, diversity were depressed because of large numbers of Diplomonorchis /eiostomi Hopkins, I941 that dominated the parasite communities of both species. Although spot and croaker from both estuaries shared eight and six parasites, respectively, many of these non-specific parasites (generalists) were more common in both spot and croaker from one estuary than from the other. All species occurring in both hosts have indirect life cycles suggesting that the availability of certain intermediate hosts as prey was an important determinant of infection. Estuary of residence was clearly as important as host species identity in determining parasite community structure.     

Elemental composition of otoliths from Atlantic croaker along an estuarine pollution gradient

Elemental compositions of otoliths of young-of-the-year Atlantic croaker Micropogonias undulatus at stations along a pollution gradient in Galveston Bay, Texas, were compared with those of sediments and livers to establish the level of consonance between otolith and habitat chemistries. Both coupled and uncoupled trends were indicated, with the bulk of the results pointing to the need for additional research to test the working hypothesis that the otolith stores a temporal record of elemental chemistry of resident waters. Lack of simple correlations between elemental concentrations in sediment or liver and in otoliths indicate that other biological and geochemical factors influence otolith composition.     

Behavioral specialization in developing sciaenids and its relationship to morphology and habitat

Behavioral development of three species of marine sciaenid fish larvae was examined and related to their sensory morphology and habitat. Anti-predator behavior of the larvae was examined under different experimental conditions to isolate the roles of vision and mechanoreception. Spotted seatrout larvae maintained high levels of responsiveness even without visual cues but performed very poorly without mechanoreception. Loss of visual cues had no impact on the distance at which seatrout responded to the stimulus. Atlantic croaker generally performed best when vision was available. This species had low responsiveness without visual stimuli, and had smaller reactive distances when unable to use vision. Red drum were the most flexible in their use of sensory systems. For almost the entire larva period, responsiveness of red drum was equally high regardless of which sensory system was not available. In addition, reactive distances were unaffected when either visual or mechanoreceptive stimuli were eliminated. Thus, seatrout and croaker are sensory specialists, and red drum are sensory generalists. This is corroborated by previous studies on the sensory morphology of these species which showed that seatrout had more mechanosensory specialization, croaker had more visual specialization, and red drum were intermediate, with some enhancement of both systems. Behavioral data are interpreted in terms of habitat usage of the three species. Seatrout have the most restricted distribution over seagrass beds, croaker have a somewhat more flexible distribution, encompassing more open water habitats, and red drum have the most flexible range of habitats, using both vegetated and unvegetated portions of the estuary. These results indicate that even closely related species can exhibit different behaviors in order to better exploit the habitats in which they occur.     

Comparative ontogeny of the feeding apparatus of sympatric drums (Perciformes: Sciaenidae) in the Chesapeake Bay

The anatomy of the feeding apparatus in fishes, including both oral and pharyngeal jaw elements, is closely related to the ecology of a species. During ontogeny, the oral and pharyngeal jaws undergo dramatic changes. To better understand how such ontogenetic changes occur and relate to the feeding ecology of a species, ontogenetic series of four closely related members of the family Sciaenidae (Cynoscion nebulosus, Cynoscion regalis, Micropogonias undulatus, and Leiostomus xanthurus) were examined. Sciaenids were selected because as adults they exhibit considerable specialization of the feeding apparatus correlated with differences in foraging habitats. However, it is not clear when during ontogeny the structural specializations of the feeding apparatus develop, and thereby enable early life history stage (ELHS) sciaenids to partition their foraging habitats. A regression tree was recovered from the analysis and three divergences were identified during ontogeny. There are no measurable differences in elements of the feeding apparatus until the first divergence at 8.4 mm head length (HL), which was attributed to differences in average gill filament length on the second ceratobranchial. The second divergence occurred at 14.1 mm HL and was associated with premaxilla length. The final divergence occurred at 19.8 mm HL and was associated with differences in the toothed area of the fifth certatobranchial. These morphological divergences suggest that ELHS sciaenids may be structurally able to partition their foraging habitats as early as 8.4 mm HL. J. Morphol. 277:183–195, 2016. © 2015 Wiley Periodicals, Inc.     

Statistical model of variable allometric growth: otolith growth in Micropogonias furnieri(Actinopterygii, Sciaenidae)

The main objective of this study was to develop a statistical model for accurate estimates of relative growth. The method was based on identifying patterns of the residuals obtained from the Huxley's allometric equation. Three different approaches were applied: (1) growth with variable proportionality and constant allometry coefficient, (2) growth with constant proportionality and variable allometry coefficient and (3) distinct growth phases in which proportionality and allometry coefficients remained constant. The proposed statistical models were applied to the relationship of the otolith size and fish size of whitemouth croaker Micropogonias furnieri . The best fit was obtained when using approach (3). A change in the growth parameters was associated with the attainment of sexual maturity.     

Sensory development and concurrent behavioural changes in Atlantic croaker larvae

Development of the visual and mechanosensory systems of Atlantic croaker larvae was examined and compared to behavioural performance in order to determine sensory system functionality. Early larvae were characterized by a photopic visual system with a high density of cone photoreceptors, but no rods or photoreceptor summation on to higher order cells. Acuity of small larvae was comparable to other species. The mechanosensory system of early larvae consisted of a relatively high density of free neuromasts on the head and body. By approximately 10 mm total length ( L _T), many sensory attributes of larvae had changed. Visual acuity had improved to levels slightly better than in other species. Rods began forming and summation ratios increased, indicating development of scotopic vision. Cephalic lateral-line canals began to enclose at 15 mm L _T and were complete by 24 mm. The trunk lateral-line began to enclose at 30 mm and was complete by 40 mm. Behavioural performance was tested using an artificial predatory stimulus under different conditions to isolate the roles of vision and mechanoreception. Both sensory systems were necessary to elicit the highest levels of responsiveness. Responsiveness of larvae <6mm was equally influenced by visual and neuromast input, while responsiveness of larvae > 6 mm was largely influenced by visual input. Both vision and mechanoreception influenced ontogenetic changes in reactive distance of larvae. When there was no visual input, reactive distances increased slightly through ontogeny, indicating the use of mechanoreception. Only when mechanoreception was blocked, the ontogenetic increase in reactive distances was greater than that of larvae with all sensory systems intact. These results indicate that Atlantic croaker larvae use both sensory systems throughout the larval period, but the relative importance of these sensory systems changes with ontogeny.     

Movements and growth of tagged young-of-the-year Atlantic croaker (Micropogonias undulatus L.) in restored and reference marsh creeks in Delaware Bay, USA

The residence time, movements, and growth of tagged young-of-the-year Atlantic croaker, Micropogonias undulatus L., were studied from July to October 1998 as measures of the success of a marsh restoration project adjacent to Delaware Bay. A total of 8173 croaker (41-121 mm SL) were tagged from each of two creeks in both marshes during July and August with internal sequential coded wire microtags. A prior tag-retention study in the laboratory found a 95% tag retention rate. Of those tagged, 3.6% were recaptured within and nearby the study creeks using seines, otter trawls, and weirs during a 105-day period. Recapture percentages ranged from 1.5% to 6.1% in individual creeks in the restored marsh. There was some movement of tagged fish between creeks in the restored marsh and out into the main creek, but 95% of the recaptures were made in the subtidal and intertidal portions of the same creek in which they were tagged. Fewer fish were recaptured at the reference marsh (1.6% recapture; n=1489 tagged) up to 50 days after tagging, with no evidence of movement between creeks. The average individual growth rates for recaptured croaker was the same in both restored (0.69 mm/day) and reference (0.63 mm/day) marshes before egress from the creeks in September and October. As a result, both created creeks in a restored marsh and natural creeks in a reference marsh appeared to be utilized as young-of-the-year habitat in a similar way during the summer and until egress out of the marshes during the fall, thus this restoration effort has been successful in creating suitable habitat for Atlantic croaker.     

Melano-macrophage centres in whitemouth croaker, Micropogonius furnieri, as biological indicators of environmental changes

Quantitative analysis of the melano-macrophage centres in the Micropogonius furnieri were made. The results obtained showed a stimulation of the mononuclear phagocytic system related to the presence of contaminants.