User:Rmcew

The article that I will be reviewing is Crucian Carp, more specifically to add a subsection detailing the morphological changes associated with hypoxia tolerance in these fish.

Wikipedia update: Anoxia & Hypoxia Tolerance

Proposed article to change: Crucian Carp

Note: Dr. Milligan, after emailing you I decided to switch my topic to cover the physiological (not strictly physiological) changes involved in anoxia and hypoxia tolerance in order to avoid sounding redundant when determining what needed to be added to the page. I could not edit my choice of topic that is positioned above this critique

Critique

The current wikipedia page dedicated to the crucian carp currently provides a brief overview of the fish’s size, colour and body shape. Building on that, the commercial uses and comparisons to goldfish are also made apparent. However, upon reading the current crucian carp wikipedia page, there is no mention of crucian carp being hypoxia tolerant, let alone anoxia tolerant. It is unclear as to why hypoxic and anoxic tolerance has not yet appeared on the page. The references section of the page cites a book chapter that provides an overview of anoxic tolerance in crucian carp based on information derived from scientific findings. Furthermore, the page discusses changes in body morphology useful during predator evasion, but fails to shed any light upon the morphological changes that arise due to hypoxic conditions.

Crucian carp are remarkable fish given the fact they are tolerant of extremely hypoxic and even anoxic conditions, a characteristic that is not widely observed in vertebrates. Furthermore, acclimation to hypoxic and anoxic conditions is achieved in different ways, indicating that these fish are quite talented physiologically. In the face of hypoxic conditions, crucian carp undergo significant morphological changes with respect to gill structure to maximize oxygen uptake. More recently, these changes have further been examined at cellular and molecular levels as well to further elucidate the hypoxic response.

On the other hand, crucian carp are capable of remaining active during anoxia. It is worth noting that because many crucian carp live in lakes and ponds, these fish are incapable of avoiding anoxia during winter. As a result, anoxic tolerance is absolutely necessary to live more than a year in aquatic environments that freeze over seasonally. This is quite a feat considering that humans would die within minutes of exposure to anoxic conditions, yet, this extraordinary ability remains in the dark from wikipedia users. Seeing as anoxia tolerance is a fundamental part of the crucian carp's life strategy it should already be mentioned in the introductory paragraphs present on the wikipedia page.

Perhaps what is even more fascinating, is that these physiological changes to hypoxia and anoxia are reversible based on the current amount of oxygen present in the environment. Consequently, it seems long overdue that the crucian carp be recognized for its tremendous ability to cope with little to none environmental oxygen.

Three Key references to support the above critique

1. Hypoxia induces adaptive and reversible gross morphological changes in crucian carp gills

As described in the title, Sollid et al. (2003) provide readers with an in-depth look at the reversible morphological changes associated with hypoxia exposure and attempt to explain these changes based on what is happenning at the cellular level. The relevant findings are

• An increase in the proportion of cells undergoing apoptosis, or programmed cell death after 3 days of hypoxia leads to a decrease in gill filament thickness and interlamellar cellular mass (ILCM)
• Apoptosis returns to normoxic levels after 7 days, suggesting that minimum ILCM is reached after 3 days
• Decrease in ILCM increases the length of protruding lamellae epithelium (respiratory surface area) that is exposed to water that flows across the gills. Effectively increasing the surface area (~7.5 fold increase) over which oxygen can be absorbed by the crucian carp
• This morphological response in the gills impedes the crucian carp's ability to maintain normoxic plasma ion levels.

2. Cell Proliferation and gill morphology in anoxic crucian carp

This study explored the morphological changes as a result of anoxic exposure, cell proliferation in select organs during anoxia and whether crucian carp cells are capable of undergoing DNA synthesis during anoxic bouts.The relevant findings are:

• Anoxic gills are indistinguishable from normoxic gills following 7 days of anoxic exposur
• Cell proliferation in gills significantly decreased in anoxic conditions, but did not significantly increase during rexoygenation. Cell proliferation was maintained at minimal levels and the amount cells in G₀ phase significantly increased, indicating cell cycle arrest but also retain the ability to undergo mitosis upon reoxygenation
• Cell proliferation in the intestine significantly decreased, and consequently increased during reoxygenation. Cell proliferation did not change in the liver. Changes in intestine cell proliferation may reflect the reactivation of the digestive tract following anoxic overwintering in frozen lakes or ponds

3. Proteomic changes in the crucian carp brain during exposure to anoxia

This study was conducted to determine whether or not selective protein transcription occurs in crucian carp brains during anoxic bouts. The relevant findings are:

• Fructose bisphosphate aldolase, GADPH, trioephosphate isomerase and lactate dehydrogenase expression is decreased. These enzymes are involved in the later reactions during glycolysis, reflecting reduced energy consumption during anoxia.
• Decrease in VDAC expression (a mitochondrial protein involved in apoptosis and necrosis pathways) was significantly reduced. As a result the brain depresses cell death during anoxia.
• Proependymin expression was increased during anoxia. This protein is involved in memory formation, learning, neuron growth/regeneration and can depress apoptosis.
• During anoxia, crucian carp brain alters proteomic expression in order to down regulate metabolism and cell death, while upregulating proependymin.