Prevalence, Morpho-Histopathological Identification, Clinical Picture, and the Role of Lernanthropus kroyeri to Alleviate the Zinc Toxicity in Moron labrax

Abstract

The present context is a pioneer attempt to verify the ability of copepod, Lernanthropus kroyeri (L. kroyeri), to uptake and accumulate heavy metals. We primarily assess the prevalence of the parasite in various seasons and its clinical signs, as well as post-mortem changes in sea bass (Moron labrax). The morphological features of the parasite using a light microscope, the bioaccumulation of heavy metals in the tissues of both L. kroyeri and M. labrax (gills, muscles) using Flame Atomic Absorption Spectrometry, and the histopathological alterations were monitored. Fish (n = 200) were obtained from Ezbet Elborg and examined for the parasite, L. kroyeri. The results revealed that the total infection was recorded at 86%. The infested fish exhibited excessive mucous and ulceration at the site of attachment. The post-mortem lesion in the gills revealed a marbling appearance with destructed filaments. Various heavy metals (Zn, Co, Cu, and Cd) were detected in the tissues of L. kroyeri and M. labrax and, surprisingly, L. kroyeri had the ability to uptake and accumulate a high amount of Zn in its tissues. Infested fish accumulated a lower concentration of Zn in their tissue compared with the non-infested ones. Within the host tissue, the accumulation of Zn was higher in the gills compared with the muscles. The histopathological findings demonstrated scattered parasitic elements with the destruction of the gill lamellae. Taken together, we highlight the potential role of L. kroyeri to eliminate Zn and it can be utilized as a bio-indicator for metal monitoring studies for sustaining aquaculture.

Keywords: Lernanthropus parasite; Moron labra; heavy metal residues; histopathology.

Figure 4

Seasonal prevalence of L. kroyeri infestation among the examined M. lebrax fish along the monitored seasons. Bars demonstrate the percentage of infested fish in each season.

Figure 5

Mean ± SEM concentration of Zn in the gills, muscle, and parasitic tissue. (****) indicates significant differences at p value > 0.0001 as reported via t-test.

Figure 1

Moron labrax showing hemorrhagic areas on different parts of the body surface (red arrows), a marbling appearance (white arrows), and gill tips that were attached in some areas with mucous secretion, and the parasites were seen by naked eyes as black filaments (black arrows).

Figure 2

Fresh samples of the parasite, L. kroyeri, appeared white to yellowish color in the Petri dish. The female was easily recognized by the presence of the two egg-sacs (arrows).

Figure 3

(A): L. kroyeri premature stage. (B): male L. kroyeri. (C): female L. kroyeri. a1; 1st antenna. a2; 2nd antenna. L1; 1st thoracic leg. L2; 2nd thoracic leg. L3; 3rd thoracic leg. L4; 4th thoracic leg. m; maxilliped. mt; mouth tube. es; egg sac. ss; spermatophore sac. up; uropod. Scale bars = 500 μm.

Figure 6

Photomicrograph of M. labrax gills stained with H&E. (A) Parasitic elements embedded between gill filaments (arrows) with stunted, bent, and disorganized primary filaments (arrowhead). (B) High power of the previous picture showing parasitic sections (arrows) with partial destruction of the lamellar epithelium (arrowhead) or metaplasia to mucus-secreting cells. (C) Gills showing parasitic sections (thin arrow), intense hemorrhage on the gill surface (arrowhead), and mucous exudate (thick arrow). (D) Gills showing denuded of primary filaments (arrow) with complete destruction of the secondary lamellae of some filaments. Scale bar = 100 µm.

Figure 7

Photomicrograph of M. labrax gills stained with H&E. (A) Showing compensatory hyperplasia and hypertrophy of the secondary lamellar epithelium (arrow) of some adjacent gill filaments. (B) Gill arch showing telangiectasis of blood vessels (arrow) and edema (arrowhead). (C) Gill arch showing partial sloughing of the epidermal covering (arrowhead) and metaplasia of the mucus secretory cells (goblet cells) in superficial cells (arrow). (D) Gill raker showing erosion of the covering epithelium (arrow) with necrosis and partial hyalinization of muscles (arrowhead). Scale bar = 100 µm.