Journal of Agricultural Extension and Rural Economics

JOURNAL OF AGRICULTURAL EXTENSION AND RURAL ECONOMICS
Integrity Research Journals

Model: Open Access/Peer Reviewed
DOI: 10.31248/JAERE
Start Year: 2024
Email: jaere@integrityresjournals.org

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Occurrence and market value implication of Melanosis (black spot) in five shrimp species wild-caught in Nigerian Coastal Waters

https://doi.org/10.31248/JAERE2025.020   |   Article Number: A8527B641   |   Vol.2 (4) - October 2025

Received Date: 13 June 2025   |   Accepted Date: 29 July 2025  |   Published Date: 30 October 2025

Authors:  Oluwafemi Paul OLUWAJANA* and Olugbemiga Peter EYITAYO

Keywords: Black spot, melanosis, Nigerian coastal waters, shrimps, sodium metabisulphite.

ABSTRACT

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The study investigated the occurrence and market value implications of melanosis in five shrimp species caught in Nigerian Coastal waters by thirty-six vessels of an Industrial Shrimping Company in Lagos, Nigeria, over twelve months (January 2024 - December 2024). All Black Tiger shrimps (Penaeus monodon), White shrimps (Penaeus notialis), Brown shrimps (Parapenaeopsis atlantica), Flower Tiger shrimps (Penaeus kerathurus), and Rainbow shrimps (Parapenaeopsis sculptilis) were treated with a solution of 3kg Food grade Sodium metabisulphite (E-223) powder dissolved in 50litres of water to prevent melanosis. All P. monodon and P. notialis, P. kerathurus and P. atlantica weighing 25g-400g each were dipped for 10minutes. P. notialis, P. kerathurus and P. atlantica, weighing 5g-15g each, were dipped for 8 minutes, respectively, while all P. sculptilis were dipped for 15 minutes. Shrimps were deep frozen on board and weighed 2 kg each into absorbent packets. Shrimps were visually assessed for signs of melanosis upon arrival. Data were subjected to Analysis of Variance (ANOVA) using SPSS v 23 and Fisher’s Least Significant Difference. A total of 596 packets (1192kg) had the occurrence of melanosis (black spots). There is no significant difference between black tiger shrimps (29±9.07) and white shrimps (30.33±8.19) in the means, but they were significantly different from brown shrimps (35.75±17.33) at P<0.05. 6W (9g-11g) grade of white shrimps had 4.3% as the highest occurrence of melanosis among all five shrimp species.  The emergence of melanosis hits its peak level in April 2024, with over 450kg of shrimps having black spots. The mean loss recorded for black tiger shrimps sales (NGN 584561.8± NGN335.27) was significantly different from that of brown shrimps (NGN 335906± NGN155.97). A total loss of NGN 7,729,908.30 was recorded in sales of the five shrimp species. The 0.11% occurrence of melanosis led to a reduction of the market value of the shrimps.

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