F.A.T. Spanings

Arachidonic acid reduces the stress response of gilthead seabream Sparus aurata L.

SUMMARY In this study the influence of the dietary level of the fatty acid arachidonic acid (ArA, 20:4n-6) was determined on the acute stress response and osmoregulation of adult gilthead seabream Sparus aurata L. Seabream were fed a diet containing either 0.9% or 2.4% of total fatty acids as ArA for 18 days before being subjected to a 5 min period of net confinement. Prior to this stressor, a subgroup of fish from both dietary treatment groups was treated with acetylsalicylic acid (ASA), an irreversible blocker of cyclooxygenase (COX). This would indicate whether any effects were caused by an enhanced synthesis of prostaglandins derived from ArA. The highest ArA levels were found in the kidneys, and these were further enhanced by dietary ArA-supplementation. In gill tissues, there were significant changes in all selected fatty acid classes 24 h after confinement, except for the docosahexaenoic acid (DHA, 22:6n-3): eicosapentaenoic acid (EPA, 20:5n-3) ratio. ArA feeding strongly reduced the cortisol response to confinement, which was partially counteracted by ASA treatment. ArA also attenuated the stress-associated increase in plasma osmolality and, in combination with ASA, enhanced the osmolality and plasma chloride levels, but reduced plasma sodium levels after confinement. Furthermore, ArA enhanced the branchial Na+, K+-ATPase activity both before and after confinement, whereas feeding ASA diminished this effect. It appeared that the effects of ArA-supplementation could not always be ascribed to an increase in prostaglandin synthesis. It is advisable to determine the long-term effects of replacing fish oils in commercial diets with vegetable oils that contain no long-chain fatty acids, particularly in carnivorous/marine species with low fatty acid elongation and desaturation activities. The effects of a low dietary intake of ArA (and other polyunsaturated fatty acids) should be studied over a longer term, taking into account any consequences for the health of the fish.

Effects of low water pH on lead toxicity to early life stages of the common carp (Cyprinus carpio)

Carp eggs were exposed immediately after fertilization to Pb concentrations of 0.12 to 0.96 μmol l−1 at water pH 7.5 and 5.6. At regular intervals mortality, the incidence of spinal cord deformation, heart rate, body movements, hatching success, and whole body concentration of K, Na, Mg, Ca, and Pb were assessed. At pH 7.5, Pb increased heart rate, and decreased body movements, while at pH 5.6, Pb also reduced hatching success, caused spinal cord deformation, decreased net Ca2+ uptake, and increased mortality of the larvae, in a concentration-dependent manner. In controls of pH 5.6 no significant changes of any of the above parameters were observed when compared to controls at pH 7.5.

Background adaptation and water acidification affect pigmentation and stress physiology of tilapia, Oreochromis mossambicus.

The ability to adjust skin darkness to the background is a common phenomenon in fish. The hormone alpha-melanophore-stimulating hormone (alphaMSH) enhances skin darkening. In Mozambique tilapia, Oreochromis mossambicus L., alphaMSH acts as a corticotropic hormone during adaptation to water with a low pH, in addition to its role in skin colouration. In the current study, we investigated the responses of this fish to these two environmental challenges when it is exposed to both simultaneously. The skin darkening of tilapia on a black background and the lightening on grey and white backgrounds are compromised in water with a low pH, indicating that the two vastly different processes both rely on alphaMSH-regulatory mechanisms. If the water is acidified after 25 days of undisturbed background adaptation, fish showed a transient pigmentation change but recovered after two days and continued the adaptation of their skin darkness to match the background. Black backgrounds are experienced by tilapia as more stressful than grey or white backgrounds both in neutral and in low pH water. A decrease of water pH from 7.8 to 4.5 applied over a two-day period was not experienced as stressful when combined with background adaptation, based on unchanged plasma pH and plasma alphaMSH, and Na levels. However, when water pH was lowered after 25 days of undisturbed background adaptation, particularly alphaMSH levels increased chronically. In these fish, plasma pH and Na levels had decreased, indicating a reduced capacity to maintain ion-homeostasis, implicating that the fish indeed experience stress. We conclude that simultaneous exposure to these two types of stressor has a lower impact on the physiology of tilapia than subsequent exposure to the stressors.

Effects of water pH on chromium toxicity to early life stages of the common carp (Cyprinus carpio)

Abstract Immediately after fertilization carp eggs were exposed to Cr(VI) concentrations of 3.9 and 9.6 μmol · l −1 at water pH 7.8 and 6.3. At regular intervals mortality, the incidence of spinal cord deformation, heart rate, tail movements, hatching success, whole body concentration of K, Na, Mg, Ca, and Cr, and ultrastructure of skin and gills were assessed. No effects of Cr on any of the examined parameters were observed at pH 7.8, while 9.6 μmol · l −1 Cr at pH 6.3 decreased total Na concentration of larvae, and increased mortality of the larvae. Skin of larvae (144-h) exposed to 9.6 μmol · l −1 at pH 6.3 showed increased numbers of mucus-secreting cells. The gill epithelium had a wrinkled appearance, and dark circle-shaped spaces, probably of mucus cells, were seen. After 240 h, the larvae were almost completely covered with mucus. In controls at pH 6.3 no significant changes of any of the above parameters were observed when compared to controls at pH 7.8.