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Fundulus grandis is a member of the Fundulus genus and is considered to be one of the largest members because it is capable of growing up to 18cm while the majority of other Fundulus reach a maximum length of 10cm. Fundulus is from the Latin meaning "bottom"; while grandis means "large". Therefore, F. grandis is the largest minnows that are preyed upon by many sports fish such as flounder, speckled trout, and red snapper. F. grandis, also commonly known as the Gulf killifish, is native to the areas spanning from Texas to Florida in the Gulf of Mexico and the eastern coast of Florida to Cuba in the Atlantic Ocean. Threats to the ultimate survivorship of the gulf killifish include extreme salinities, temperatures, and toxic events such as naturally occurring ones like the Dead zone in Louisiana and man-made ones like the Deepwater Horizon oil spill.

Coloration
Fundulus grandis has unique coloration that separates itself from other Fundulus. First, the base color is a dull greenish above shading to lemon yellow below. Furthermore, there are differences in coloration between males, which show much more vivid colors with silver flecking and noticeable striping; and females, which can appear olive to dull olive below if they grow big enough. Additionally, there are stripes, spots, and different colors along the body structure. In the predorsal region, there are predorsal stripes, which maybe present but generally fade as the fish ages and occasionally predorsal spots. There are also small pearly spots along the side of the fish. In regards to different coloration along the body structure, the anal and lower half of the caudal region may be yellow or the anal, dorsal, and caudal regions may be darker in color with white splotches at the base. Additionally the coloration of the male fish is affected by seasonality because their color changes when they are breeding. In all, these males are deep blue dorsally, and have blue-median fins with light blue spots and yellow-orange margins. However, in general, the gulf killifish is characterized by its’ yellowish or pale below, and darker back with many pale spots, mottling and inconspicuous bars.

General Counts of body structures
There are more than 15 scale rows on the killifish’s body between the pelvic fin to the isthmus; as well as, anywhere from 31-39 longitudinal scale rows. Additionally, there are on average 17-20 individual scales around the caudal peduncle. There are also anywhere from 12-19 faint stripes along the side of the killifish. The killifish also has 5 pairs of mandibular pores, which are sensory pores located on the underside of the lower jaw that are part of the lateral line sensory system. In terms of number of common body structures, there are around 9-12 gill rakes, 10-12 dorsal rays, 9-11 anal rays, and 6 pelvic rays.

Average Body Shape and Size
The maximum length of the gulf killifish is 18.0 cm, but a common length is around 10.4 cm. These fish are characterized by a blunt head and short snout. The mouth is positioned nearly terminal and its lower jaw slightly projects outwards. However, the eyes of the gulf killifish go fewer than 1.5 times in snout. The position of the dorsal varies slightly among individuals, yet it generally originates anterior to the anal fin origin. The anal fin of the killifish is rounded and the base of the fin is more than half the length of its longest rays. The distance from the origin of the dorsal fin to the end of the hypural plate is usually less than the distance from the origin of the dorsal fin to the preopercle; yet occasionally these distances are equal due to the genetic variability among individuals. An important characteristic of the fish is the length of the gill slit because it determines how much water can ultimately pass through the gills. The anterior edge of a gill slit is motile, moving outward to allow water to exit, but closing to prevent reverse flow. For gulf killifish, their gill slit extends dorsal to the uppermost pectoral fin ray. In all, the gulf killifish is one of the largest killifish species with a blunt head and short snout.

Types of Habitats
The gulf killifish can survive in wide ranges of habitats because it is highly adaptive. These adaptions have changed over time through evolution, which have allowed for the increased survival of the gulf killifish. These different habitats include: estuarine, lowland, upland, coastal marshes, lagoons, rivers, and streams. The majority of the time the gulf killifish spends time around brackish water near coasts.

Native Areas
The gulf killifish is found in several bodies of water including: the Atlantic Ocean, the Gulf of Mexico, the Caribbean Sea, and the Southeast United States Continental Shelf. The normal range of gulf killifish is from Texas to the western coast of Florida and from the east coast of Florida to Cuba. These waters undergo several changes in water characteristics such as temperature, dissolved oxygen, and salinity among many other variables that can have profound effects on the survival and abundance of the gulf killifish.

Salinity Ranges
Spending a lot of time near the coasts ensures that the gulf killifish is able to survive salinity ranges including freshwater because their habitats get influx of freshwater into the ecosystems normally. The gulf killifish is able to withstand salinity ranges from freshwater or 0ppt, thought 76 ppt. This is a relatively wide range of salinity but adaptations have allowed these important characteristics for survival. However, there are threats to the survival of the gulf killifish because of changes in salinity. Salinity has profound effects on the development and hatching of gulf killifish eggs. One of the secondary effects of the Deepwater Horizon oil spill was the opening of industrial canals to send freshwater into the gulf in order to push the oil away from the marshes of Louisiana. This caused the salinity to drip quickly within some of the gulf killifish's habitat, which caused problems that had not been expected. One of these unexpected problems was that many eggs remained unhatched because the salinity levels had dropped to below the critical salinity level where hatching can still occur. Another study done by Patterson et al. in 2012 looked into how salinity affects the survivorship and body size of fish within different salinities. The results from this study showed that the fish brought up in the lower salinity were less likely to survive as well as have much lower body size and growth. These studies showed how importance of salinity on the survival of the gulf killifish.

Temperature Ranges
The normal climate for the gulf killifish is tropical, as would be expected from where the fish is usually found. However, the gulf killifish is able to survive in temperatures ranging from 5 degrees Celsius to 37 degrees Celsius. Temperature plays an important role in the hatching of viable eggs as well as the relative abundance of these eggs. One study done by Gothreaux and Green found that lower water temperature with the use of shade in the months of June, July, and August lead to the highest number and most viable eggs. However, in the month of September, when the water temperature has begun to drop, the extra shading leads to much lower temperatures that lead to significantly fewer and less viable eggs. This study and many like it have shown that temperature can have profound effects on the overall survivorship of the gulf killifish.

Dissolved Oxygen
Another key characteristic of the habitats, which is influential to the survival of gulf killifish, is the amount of dissolved oxygen. Fish need oxygen to survive and carry out normal activities and processes. Lower levels of oxygen, or hypoxia, is common in near-shore environments, one of the main habitats of the gulf killifish. These hypoxic conditions may last from several hours to several days, which means that the gulf killifish must be able to adapted to survive these conditions. The gulf killifish utilize different ways to cope with hypoxia including: behavioral changes, physiological changes, and changes to biochemical processes. One main threat because it decreases the levels of dissolved oxygen is the Louisiana Dead Zone, which causes a large amount of fish kill every year. This dead zone results from nutrient and chemical-rich water from the Mississippi River Valley Basin entering the Gulf of Mexico. This eutrophicated water ultimately leads to no dissolved oxygen remaining within the ecosystem because of increased activities of algae and decomposers. Therefore, the fish that remain will end up dead because of the lack of oxygen. One study done by Love and Rees showed that fish collected during the summer months were better suited to hypoxic conditions because they were already acclimated with the lower levels of dissolved oxygen more so than any other season. Due to the higher temperatures during the summer months, there is less dissolved oxygen within the ecosystem.