Dimitris G. Sfakianakis

Effect of heavy metals on fish larvae deformities: A review

Heavy metals have been associated with many fish deformities in natural populations and in laboratory produced specimens as well. Deformities in general have devastating effects on fish populations since they affect the survival, the growth rates, the welfare and their external image. Although the embryonic stage in respect to heavy metal exposure has been extensively studied, there is not much information available as to what happens in fish larvae and adults. In the present article, we present the available information on the effect of heavy metals on fish larvae deformities. We also address the need for more research towards the effects of metals on the subsequent life stages in order to assess the long-term consequences of heavy metal poisoning on fish organisms and possibly correlate these consequences with the environmental contamination (use as biomarkers).

Development of a saddleback-like syndrome in reared white seabream Diplodus sargus (Linnaeus, 1758)

Depression of the dorsal profile accompanied by kyphosis and, in most of the cases, haemal lordosis was observed in reared Diplodus sargus. The ontogeny and the anatomy of deformity are presented and the probable causative factors are discussed.

The effect of rearing temperature on body shape and meristic characters in zebrafish (Danio rerio) juveniles

Although zebrafish (Danio rerio) is a highly studied organism on many fields of research, many aspects of its basic biology still elude the scientific community. Its response to temperature - especially developmental one - has been very scarcely studied and this is an important lack of knowledge since the species is considered quite eurythermal in nature. In the present study, zebrafish was subjected to four different developmental temperatures (22, 25, 28 and 31°C) from the half-epiboly stage until after metamorphosis in order to examine whether the temperature can influence the juvenile’s phenotype. Morphometric and meristic characters were explored. Body shape and almost all of the meristic characters studied were significantly affected by the temperature applied during the first stages of development. Most meristic characters of the study, presented a significant differentiation in the extreme temperatures used (22 and/or 31°C), whereas lower temperatures seemed to produce higher meristic counts in the majority of the characters. Zebrafish juveniles, as shown in this study, exhibit highly variable phenotypes (phenotypic plasticity) induced by diverse thermal conditions during their early ontogenetic stages possibly in order to successfully adjust to different environments.

Morphological differences between wild and farmed Mediterranean fish

Gilthead seabream (Sparus aurata L.) and European seabass (Dicentrarchus labrax L.) are important commercial marine fish species both for aquaculture and fisheries in the Mediterranean. It is known that farmed individuals escape from farm facilities, but the extent of escape events is not easy to report and estimate because of the difficulty to distinguish between wild and farmed individuals. In this study, significant differences provided through morphometry evidence that the cranial and body regions of seabream and seabass are different regarding their farm or wild origin at different scales. Morphological variations have been shown to be a valuable tool for describing changes in shape features. Therefore, the biomass contribution of escapees to local habitats could be determined by identifying escaped individuals from fisheries landings as a first step to assess the potential negative effects of fish farm escapees on the environment, and their influence on wild stocks and local fisheries.

Discriminating farmed gilthead sea bream Sparus aurata and European sea bass Dicentrarchus labrax from wild stocks through scales and otoliths.

The study of mass and standard length (L(S) ) relationships showed that farmed individuals had higher values than wild fishes for both gilthead sea bream Sparus aurata and European sea bass Dicentrarchus labrax. Such differences were more pronounced in larger individuals than smaller ones and were more noticeable in S. aurata than in D. labrax. Additionally, differences in external characteristics of scales were detected between origins. A high proportion of farmed S. aurata had a regenerated nucleus (98%) and scale malformations (73%), and there were no annual rings in the farmed D. labrax (100%). Variation in otolith morphology was examined through shape descriptors such as area, perimeter, circularity, roundness, mass, height and length relationship and elliptic Fourier descriptors (EFDs). Important differences were found within geographical origins according to each shape descriptor separately, but no clear patterns distinguished wild and farmed fish. Discriminant analysis with either all shape descriptors together or EFDs was able to classify with high accuracy both S. aurata (89·5-95·7%) and D. labrax (93·2-95·2%) according to their origin. Hence, this study suggests the use of scale characteristics as the easiest and quickest way to distinguish farmed or escaped fishes, and secondly, the usefulness of EFDs or shape descriptors to improve such separation.

Effect of developmental temperature on swimming performance of zebrafish (Danio rerio) juveniles

It is widely known that water temperature affects the swimming capacity of fish. But the effect of the rearing temperature on the swimming ability of the fish at later stages, has not had similar attention. In this study, four populations of zebrafish, were reared in different water temperatures (22, 25, 28 and 31°C) and after being acclimatized in a common temperature (26.5°C) for over a month, they were subjected to swimming trials in order to evaluate the maximum relative critical velocity (RUcrit) in each case. Fish that were reared in 22°C showed statistically significant lower performance than the ones reared in 31°C (7.72 ± 0.17 vs. 8.79 ± 0.28, means ± S.E.). Possible explanations for the observed differentiation could be the effect of early life temperature on fish muscle ontogeny or on body shape.

Nonlinear responses to waterborne cadmium exposure in zebrafish. An in vivo study

Abstract Cadmium (Cd) has proved to be associated with numerous toxic effects in aquatic organisms via waterborne exposure. With a view to investigate Cd toxicity along a broad spectrum of exposures reaching from environmental to toxic, we employed adult zebrafish (Danio rerio) for an in vivo study. A number of 10 fish per tank were placed in 40 L tanks and were exposed for 30 days to 0.0, 5.0, 25, 50, 75, 100 and 1000 &mgr;g Cd per liter. There were 2 tanks for each Cd exposure (duplicate experiment). Mortality was recorded daily, dead fish were collected and tissue samples were obtained for histologic observation, whereas remaining tissues were stored for Cd burden determination. Surviving fish were collected at the end of the experiment. Median overall survival (OS) in days was found to be 9.0, 11.0, 8.0 and 7.0 for 25 &mgr;g/L, 50 &mgr;g/L, 75 &mgr;g/L and 100 &mgr;g/L respectively, with all of them showing mortality greater than 50%. Remarkably, fish exposed to the highest Cd concentration (1000 &mgr;g/L) survived the longest exhibiting a mean OS of 29.2 days. Cd determination in fish tissue was conducted with an in house ICP‐MS method and levels ranged from 3.1 to 29.1 ng/mg. Log Cd tissue levels were significantly correlated with the log Cd exposure levels (r = 0.535, p < 0.001). The highest Cd burden was determined for fish exposed to 1000 &mgr;g Cd /L (mean = 12.2 ng/mg). Histopathology supported these results. Our findings disclose a deviation in toxic responses through the range of Cd concentrations, leading to nonlinear responses. These differentiated responses, could be linked to hormesis phenomena. Graphical abstract Figure. No Caption available. HighlightsTissue Cd accumulation is dose dependent but not time dependent.Fish exposed to the highest administered exposure survived the longest.Histopathological findings support nonlinear responses.Unanticipated mortality and histopathology responses in zebrafish could be associated to hormesis phenomena.High dose exposure resulting in less adverse effects is attributed to mechanisms stimulated at low doses.

Are zebrafish Danio rerio males better swimmers than females

Swimming performance of zebrafish Danio rerio males and females initially reared in four different temperatures was assessed by measuring their relative critical swimming speed after acclimation to a common temperature. Males reared at 31° C achieved higher swimming speeds than females reared at the same temperature. Morphometric measurements indicate differences in body shape between sexes that could account for the difference in swimming speed.

Ontogeny of the body skeleton in Seriola dumerili (Risso, 1810)

Abstract Osteological development of Seriola dumerili is described and illustrated based on 141 specimens (3.9–27.0 mm TL) reared under semi-intensive culture conditions (Greece). The ontogeny of the vertebral column started with the formation of the neural arches (4.6 mm TL) and continued with the haemal arches and the centrum (4.8 mm TL). Until the end of the study, the centrum (12.5 mm TL) and neural arches (23.8 mm TL) were fully formed, while the haemal arches were not. The first skeletal elements of the fins started developing in the pectoral (3.9 mm TL), anal (4.8 mm TL), caudal (4.8 mm TL), dorsal (6.0 mm TL) and pelvic fins (6.3 mm TL), while the fin rays followed a slightly different pattern pectoral (5.6 mm TL), caudal (5.3 mm TL), anal (6.2 mm TL), dorsal (6.3 mm TL) and pelvic fin rays (7.0 mm TL). The ontogeny of the skeletal parts are compared with those of other Carangidae and Teleosts.

Exercise–related muscle lactate metabolism in zebrafish juveniles: The effect of early life temperature

Abstract The accumulation of lactate in fish muscles during exercise and particularly its decomposition rate afterwards is a process of great importance, as it significantly influences swimming capacity. In the present study, zebrafish juveniles were reared at different water temperatures (22°C, 25°C, 28°C and 31°C) and before being subjected to the swimming trials (according to Bretts method) they were acclimated to a common intermediate temperature of 26.5°C for 45 days. Muscle lactate concentration was estimated on 35 specimens per temperature origin, which were sampled at the following time periods: at rest, after full exhaustion due to swimming and after recovery for thirty minutes, one hour, three hours, six hours and nine hours. Lactate analysis revealed that in all cases, lactate metabolism follows that previously described for other species patterns, since its concentration rises during exercise and decreases during the recovery time. It was also shown that developmental temperature affects not only the initial and final lactate concentration (at rest and at full exhaustion respectively), but its decomposition rate during recovery as well since the 22°C-reared fish require considerably more time than the others in order to fully recover and the 31°C-reared fish present the fastest recovery among all. Developmental temperature during the early life stages is once again proven to play an important role in the subsequent life of the fish.