Effect of low salinity on the yellow clam Mesodesma mactroides

Abstract

The aim of this study was to determine the lethal salinity (LC 50 ) for the yellow clam Mesodesma mactroides (Bivalvia: Mesodesmatidae) and identify histopathological alterations that could be used to diagnose structural changes in clam tissue. Clams in two size classes (adults and juveniles) were placed in 10 L chambers and exposed to salinities of 35, 30, 25, 20, 15, 10, and 5 g/L. There were triplicate chambers with seven clams each for each salinity. The LC 50 values for a 48 h exposure were 6.5 g/L and 5.7 g/L for adults and juveniles, respectively. For a 96 h exposure, the LC 50 values were 10.5 g/L for adults and 8.8 g/L for juveniles. The histological examination of yellow clams exposed to 10 g/L for 96 h showed intercellular oedema and necrotic foci in the epithelium of the digestive gland and occlusion of the lumen of the digestive gland. In conclusion, M. mactroides can be characterised as a moderately euryhaline species, tolerating salinities from 35 to 15 g/L.Keywords: yellow clam, lethal salinity, LC 50 , histology, extreme southern Brazil. Efeito da salinidade reduzida no marisco branco Mesodesma mactroidesResumo O objetivo deste estudo foi determinar a salinidade letal (CL 50 ) para o marisco branco Mesodesma mactroides (Bivalvia: Mesodesmatidae) e as alterações histopatológicas que poderiam ser úteis para o diagnóstico de mudanças estruturais no tecido dos bivalves. Mariscos de duas classes etárias de tamanha (juvenis e adultos) foram colocados em recipientes de 10 L e expostos a salinidades de 35, 30, 25, 20, 15, 10 e 5 g/L. Os tratamentos foram realizados em triplicata com sete bivalves em cada recipiente, A CL 50 para 48 h de exposição foi 6,5 g/L e 5,7 g/L para adultos e juvenis, respectivamente. Para 96 h de exposição, a CL 50 foi 10,5 g/L para adultos e 8,8 g/L para juvenis. O exame histológico dos mariscos expostos à salinidade de 10 g/L por 96 h revelou edema intracelular e focos necróticos no epitélio da glândula digestiva e oclusão da luz da glândula digestiva. Em conclusão, M. mactroides pode ser considera uma espécie eurialina moderada, tolerando salinidades de 35 até 15 g/L.Palavras-chave: marisco branco, salinidade letal, CL 50 , histologia, extremo sul do Brasil.

Effect of acute salinity stress on ion homeostasis, Na+/K+-ATPase and histological structure in sea cucumber Apostichopus japonicus

“…Integumentary system of the sea cucumber exposed a salinity of 40 psu mainly observed nucleus hypertrophy of epithelial cells, increase of mucous cells and tight arrangement of connective tissue in dermal layer. The gastrointestinal tract is particularly responsive to stressors, which can cause a variety of changes including alteration of normal protective microflora and decreased integrity of the intestinal epithelium (Longo and Díaz 2015; Carvalho et al 2015). Histological variations revealed a negative relation between decreasing salt concentration and tissue integrity.…”

Multimarker response to salinity stress in two estuarine bivalves of different genetic diversity: Mya arenaria and Limecola balthica from the Gulf of Gdańsk (southern Baltic Sea)

“…In L. balthica, changes induced by stress from hypoosmotic conditions included abnormalities of the gill epithelium, more advanced digestive system atrophy, interstitial edema in the stomach and intestine, and intracytoplasmic vacuolization swelling of the viscera. Similar structural disruptions were observed in Crassostrea gigas, Crassostreal virginica, and Mesodesma mactroides when individuals of these species were exposed to low salinities (Winstead 1995; Knowles et al 2014;Carvalho et al 2015). The abnormalities found in clams exposed to hyperosmotic conditions, except in the case of the 35 psu treatments, were overall less common and less severe than in the hypoosmotic treatments, and included erosion of lamellar epithelium of gills and vacuolation of alimentary epithelial cells.…”

“…Similar structural disruptions were observed in Crassostrea gigas, Crassostreal virginica, and Mesodesma mactroides when individuals of these species were exposed to low salinities (Winstead 1995; Knowles et al 2014;Carvalho et al 2015). In L. balthica, changes induced by stress from hypoosmotic conditions included abnormalities of the gill epithelium, more advanced digestive system atrophy, interstitial edema in the stomach and intestine, and intracytoplasmic vacuolization swelling of the viscera.…”

“…However, in the current study this response is rather unlikely since siphonal activity (i.e., extension and movements) was observed in both clam species in all salinity treatments. Therefore, this process may be responsible for poor nutrition, and may lead to death in extreme cases (Elston 1999;Carvalho et al 2015). Significant decreases in carbohydrates and glycogen were observed in the Baltic clams at the beginning of the experiment, presumably because of catabolism to provide energy for basic physiological processes during the dormant state (Guppy & Withers 1999).…”

“…This atrophy, which occurs in bivalves when conditions are stressful, often results in the loss of absorptive cells from the digestive gland. Therefore, this process may be responsible for poor nutrition, and may lead to death in extreme cases (Elston 1999;Carvalho et al 2015). Digestive gland atrophy (and in particular DTA) is, however, fully reversible once environmental conditions improve or some level of acclimatization is achieved (Winstead 1995).…”