Silvia Crespo

Ontogeny of the lymphoid organs in the turbot Scophthalmus maximus: a light and electron microscope study

Abstract A histological and ultrastructural study was made of the development of the kidney, thymus and spleen in the turbot Scophthalmus maximus , from hatching until the end of metamorphosis. Primordial haemopoietic stem cells are first observed in the pronephric kidney very early after hatch and rapidly differentiate into different cellular types. The spleen develops later, soon becoming rich in blood capillaries, red blood cells and thrombocytes. The thymus is the last lymphoid organ to appear but shows a quick development. This organ seems to originate from haemopoietic stem cells migrating from the head region of the kidney. Lymphoid organs become lymphoid in the sequence thymus, kidney and spleen. Although a small number of lymphocytes appear only in the later stages, cellular types involved in non-specific defense mechanisms, such as macrophagic and reticular cells, originate in early stages. These observations suggest that non-specific systems may play an important role in the immunocompetence mechanisms of the turbot during early larval development.

Histopathological observations during larval rearing of common dentex Dentex dentex L. (Sparidae)

Histological observations in cultured common dentex Dentex dentex larvae are described from days 1 to 36 after hatching. No alterations were found throughout the lecitotrophic period. Following subsequent experimental starvation, larvae showed atrophy of the digestive structures, pancreatic degeneration and lack of supranuclear vacuoles in the hindgut. During transition from endogenous to exogenous feeding, 30% of 7- and 8-day-old larvae and 11% of 9-day-old larvae exhibited histological alterations similar to those described in starved individuals, regardless of the level of rotifer enrichment. During the Artemia feeding period, intestinal steatosis was a common feature, mainly from day 30 onwards. Swimbladder non-inflation rates ranged from 12% to 77%. By day 17, the batch of larvae showing the highest percentage of non-inflation exhibited the lowest growth performance. Histopathological alterations associated with bacterial agents were described only occasionally. No parasites were found in any of the specimens examined. It is suggested that nutritional factors, rather than infectious agents, are responsible for the high mortality encountered in cultured dentex larvae.

Effects of the gill parasite Zeuxapta seriolae (Monogenea: Heteraxinidae) on the amberjack Seriola dumerili Risso (Teleostei: Carangidae)

Zeuxapta seriolae (Monogenea: Heteraxinidae) infection was associated with important mortalities of amberjacks (Seriola dumerili) reared in tanks in the experimental facilities of the Spanish Institute of Oceanography (Western Mediterranean) during the period 1998–2000. Fish infested by this parasite presented characteristics similar to those described for Seriola quinqueradiata parasitized by Heteraxine heterocerca in Japan. All dead amberjacks had high parasite abundance (mean abundanceFS.D.=686.7F125.4) and egg strings entangled in gills. The parasitological analysis of 17 live amberjacks collected from the infested tanks showed that 41.2% of fish harboured Z. seriolae with intensities ranging between 5 and 731 parasites per fish. No apparent relationship was observed between the abundance of the parasite and the condition factor (rS=0.175, n=17, p>0.5). However, the haematocrit values were significantly lower in the fish infested with monogeneans. The relationship between parasite abundance and haematocrit values was negative and statistically significant (rS=0.625, n=17, p<0.01). The light and scanning electron microscope studies of affected gills revealed that the parasites attached to the host grasping one or two lamellae with each clamp of the haptor, which led to lamellar synechiae, lamellar clubbing and disruption of epithelial and vascular structures. A mild to moderate epitheliocystis infection was also

Epitheliocystis disease in the cultured amberjack, Seriola dumerili Risso (Carangidae)

Abstract Epitheliocystis infection affecting the gill and the pseudobranch of the cultured amberjack, Seriola dumerili Risso, is described. In hyperinfected fish, proliferative cell response around the epitheliocystis capsule resulted in gill and pseudobranch lamellar fusion, which led to mass mortalities in the 0+age class. Histopathological and scanning electron microscope observations showed that the target cell was the chloride cell since (1) epitheliocystis organisms were first found within the chloride cell; (2) chloride cells underwent degeneration in the filament epithelium, proliferated along the lamellae, and hypertrophied; and (3) cysts were found only in the trailing edge of the gill filament and in the interlamellar spaces where, in healthy fish, chloride cells are mainly located. In some cases, the pseudobranch of infected fish was much more severely affected than the gill. It is therefore suggested that, for diagnostic purposes, the pseudobranch should also be sampled when epitheliocystis disease is suspected.

An in vitro study of the effects of zinc on osmoregulatory processes

Abstract The short-circuited opercular epithelium of seawater-adapted killifish Fundulus heteroclitus was studied following addition of zinc to both serosal and mucosal sides of the preparation. Zn inhibited the short-circuit current which is a direct measure of the chloride transport across the epithelium. Light microscope observations showed that the mucosal side of the epithelium was completely desquamated after 1 h exposure to Zn. It is suggested that desquamation of gill epithelia described by several authors following in vivo Zn contamination is a direct consequence of the breakdown of osmoregulatory processes.