The new millennium has witnessed invasive species which have a renowned and most severe ecological and economic threat globally. Asian tiger shrimp (Penaeus monodon Fabrizio) is invasive to the coastal waters of Nigeria. Although widely exploited with significant economic importance, investigation into its adaptation and potential ecological impact in the newly found environment is poorly known.
This article delves into the world of Nigerian Tiger Shrimp (Penaeus monodon), exploring their characteristics, ecological impact, and their role in aquaculture. We will examine their biology, habitat, and the challenges and opportunities they present.
Penaeus monodon
Characteristics and Identification
The giant tiger prawn inhabits the coasts of Australia, South East Asia, South Asia and East Africa. Penaeus monodon was first described by Johan Christian Fabricius in 1798. The most distinct features for identification of this species are: fifth pereiopods without exopod; hepatic carina horizontally straight; and gastroorbital carina occupying the posterior half of the distance between hepatic spine and postorbital margin of carapace.
Depending on substratum, feed and water turbidity, body colours vary from green, brown, red, grey, blue and transverse band colours on abdomen and carapace are alternated between blue or black and yellow. Females can reach about 33 cm (13 in) long, but are typically 25-30 cm (10-12 in) long and weigh 200-320 g (7-11+1⁄2 oz); males are slightly smaller at 20-25 cm (8-10 in) long and weighing 100-170 g (3+1⁄2-6 oz). The carapace and abdomen are transversely banded with alternative red and white. The antennae are grayish brown.
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Key Features:
- Rostrum well developed and toothed dorsally and ventrally
- Carapace without longitudinal or transverse sutures
- Hepatic and antennal spines pronounced
Habitat and Distribution
The black tiger shrimp is a widespread Penaeid shrimp native to the eastern hemisphere from longitude 30°E to 155°E and latitude 35°N to 35°S (Indo-West Pacific ocean of East Africa, Arabian Peninsula, India, China Japan, the Middle East and North Australia. Juveniles of P. monodon are generally found in sandy estuaries and mangroves, and upon adulthood, they move to deeper waters (0- 110 m) and live on muddy or rocky bottoms.
P. monodon is now established in many areas presumably due to escapement from aquaculture facilities outside its native range, including West Africa and South East United States. Other regions of invasion include, the Caribbean, northern and north-eastern coasts of South America.
The Nigerian coastline itself spans approximately 853 km with seven states along the coastal zones namely Lagos, Ondo, Delta, Bayelsa, Rivers, Akwa Ibom and Cross River respectively from South-west to South-South coast.
Ecological Impact and Adaptation
Generally they have great effects on native biodiversity and cause difficulties in natural ecosystems conservation and management. The first report of this incidence was about 16 years ago. The role of food and feeding habit of this shrimp cannot be overemphasized in its adaptation to novel habitat. Food must be exploited in the new environment and the adaptation for this is related to morphological traits connected to feeding.
A major source of food is phytoplankton which comprises complex community of floating micro-algae with size range from about 1 μm to a few millimetres. As primary producers, carbon in the form of carbon dioxide is needed in the aquatic environment to initiate the food chain for secondary and tertiary producers. Other essential inorganic nutrients dissolved in water are phosphates, nitrates are sulphates.
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This survey provides baseline information on the phytoplankton community and physico-chemical parameters in ten selected stations from five states where they are exploited in Nigeria.
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These include:
- Ibeno (Akwa Ibom State)
- Bonny (Rivers State)
- Kaa (Rivers State)
- Brass (Bayelsa State)
- Aiyetoro (Ondo State)
- Makoko (Lagos state)
- Folu (Lagos state)
- Apapa (Lagos state)
- Tin Can Island (Lagos state)
- Tarkwa Bay (Lagos state)
Total of 147 species of phytoplankton from six classes were recorded during the survey with diatoms being the most prevalent (70.4%), green algae (20.4%), Blue-green algae (5.6%), Chrysophyceae (1.9%). Generally, ecological factors in their newly found environment are similar to their native range.
The Physico-chemical characteristics of the study areas are presented in Tables 2 and 3. Mean temperature range was between 27.33 ± 1.53°C (station LM) and 29.00 ± 1.00°C (station RB). Mean pH values ranged between 7.39 ± 0.08 (station LA) and 8.13 ± 0.14 (station OA) (buffered ecosystems across sampling station). Range value for dissolved oxygen was 5.40 ± 3.22 mgL-1 (station AB)-8.00 ± 1.44 mgL-1 (station OA) while conductivity was 11.22 ± 10.03 μS/cm (station LM)-39.33 ± 5.87 μS/ cm (station OA). The lowest values for phosphate-phosphorus, nitratenitrogen and sulphate were 0.11 ± 0.07mgL-1 (station RK), 0.10 ± 0.07 mgL-1 (station RK) and 523.67 ± 880.21 mgL-1 (station LM) respectively.
Aquaculture and Economic Importance
Shrimp farming has been practiced for more than a century for food and the livelihood of coastal people in some Asian countries, such as Indonesia, the Philippines, Taiwan Province of China, Thailand and Viet Nam. Penaeus monodon was originally harvested together with other shrimp species from traditional trapping-growing ponds or as a significant by-product of extensive milkfish ponds.
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In 2010, Greenpeace added P. monodon to its seafood red list - "a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries".
In P. monodon, temperature is an essential environmental parameter having considerable impact not only on the success of culture, but also on survival and spread in areas of introduction. Optimum temperature range of 28°C-33°C is essential for survival and growth, but detrimental below 20°C. Apart from the temperature of coastal waters, salinity over the years has also been recognized as a key factor influencing the absence, presence and abundance of endemic species.
Countries in West Africa are generally constituted by many physico-chemical characteristics that make them environmentally sustainable for shrimp farming and coastal areas have water suitable for farming many other aquatic species. The information will be useful for aquaculture and wild resource management on the invasive species.
Nutritional Value
Black tiger shrimp is that they are high in protein but low in calories. They also contain important nutrients such as vitamins, and protein which are good for health. They are a good source of selenium. Black tiger shrimp contains 0 g of saturated fat and 170 mg of cholesterol per serving. 85 g of Black tiger shrimp contains 1.80 mg of iron, 60.35 mg of calcium.
Here's a quick look at the nutritional highlights per serving:
| Nutrient | Amount per Serving |
|---|---|
| Calories | 60 |
| Total Fat | 0.5g |
| Protein | 15g |
| Vitamin D | 0mcg |
| Calcium | 90mg |
| Iron | 0.8mg |
| Potassium | 60mg |
The locally adapted culture technology has allowed Thai farmers to overcome serious disease, environmental and trade problems and maintain its status as a leading producer. The introduction or importation of wild broodstock is commonly practiced among the major producing countries because local supplies are insufficient and domestication technology has not yet been commercially developed.
This survey on phytoplankton and physico-chemical parameters was carried out across selected station in Nigeria as a preliminary investigation to understand the ecology of the invasive tiger shrimp.
