Global warming raises surface water temperatures, impacting fish alongside pollutants, such as ubiquitous xenoestrogens. Combined stressor effects are poorly studied but likely to worsen impacts and hinder biota adaptation, warranting further research. Unadapted fish face heightened risks. The liver is a vital metabolic organ, sensitive to temperature and xenoestrogens, eventually adjusting hepatocyte size and number to ensure survival, growth, and reproduction. This study assessed, for the first time, the impact of exposure (45 days) to thermal stress (29 °C versus 26 °C) and ethinylestradiol (EE2, 5 ng/L) on male guppies, primarily on body and quantitative liver morphology. Higher temperature reduced body mass (14%) and standard length (3.6%) gain. EE2 exposure reduced body mass increase (14%), hepatosomatic index (20%), and the volumes of the liver (32%), hepatocytes (16%), and their nuclei (17%). The nucleus-to-cytoplasm ratio and total hepatocyte number remained stable. No histopathological lesions existed. Guppies appear to have adapted to stressors by reducing hepatocyte size and utilizing lipid reserves, yet they exhibited deficits in body growth and hepatosomatic index. Gonadal maturation was unaffected. Only under EE2 at 29 °C did hepatocytes show minimal lipid droplet content (less vacuolation). This indicated exhausted reserves, reinforcing how heat and toxicants interact to exacerbate impacts.

Neurotransmitters modulate gonadal maturation in bivalves. However, it remains unclear whether there are differences in the nervous system structure between sexes, maturation, and ganglia. Therefore, a stereological study was conducted on the ganglia of adult peppery furrow shell (Scrobicularia plana). Equal-sized males, females, and undifferentiated (gamete absence) animals were fixed with 10% formalin and processed for light microscopy. They were serially cut into 35 µm paraffin thick sections and stained with hematoxylin-eosin. Sections with cerebral (cerebropleural), pedal, and visceral ganglia were studied. The parameters estimated were the volumes of the ganglia, the total and relative volumes of their cortex (outer layer) and medulla (neuropil), and the total number of cells (neurons, glia, and pigmented) per ganglia and compartment. The volumes and numbers were estimated, respectively, by the Cavalieri principle and by the optical fractionator. Females show a larger glia to neuron numerical ratio. Further, females have a greater ganglionic volume than undifferentiated adults, with males showing intermediate values. These facts indicate that the ganglia size is related somehow to maturation. The cell size forms the basis of the differences because total cellularity is equal among the groups. The three ganglion types differ in total volumes and the volume ratio of the cortex versus the medulla. The greater volumes of the pedal ganglia (vis-a-vis the cerebral ones) and of the visceral ganglia (in relation to all others) imply more voluminous cortexes and medullae, but more neuronal and non-neuronal cells only in the visceral. The new fundamental data can help interpret bivalve neurophysiology.