Effects of the harmful diatom Chaetoceros concavicornis on respiration of rainbow trout Oncorhynchus mykiss

Abstract

ABSTRACT-Chaetoceros concavicornis and C. convolutus are harmful diatom species which commonly occur in many temperate coastal marine waters and which can cause finfish mortalities when present at concentrations as low as 5 cells ml-' of seawater. Death of finfish, including salmonids, by these harmful Chaetocerosspp. has been suggested to be caused by: (1) microbial infections of damaged gill tissue; (2) hemorrhage of gill capillaries; or (3) suffocation from excess mucus production at the sites of penetration of the gills by the spines. Our data indicate that the barbed spines of these diatoms damage the physical integrity of the respiratory epithelium of rainbow trout Oncorhynchus mykiss. The trout responds to this physical impairment of gill tissue by producing excessive amounts of mucus. The accumulation of this mucus on and between the secondary lamellae inhibits the gill function of O2 uptake (and likely metabolic waste products release). The hypoxic conditions which result within the fish then cause a cascade of events, including anaerobic metabolism. Trout mortalities occur coincident with severe decreases in O2 concentration and pH as well as increases in lactate and glucose concentrations of the arterial blood.

Epizootic mortality in the pilchard Sardinops sagax neopilchardus in Australia and New Zealand in 1995. I. Pathology and epizootiology

“…1985, Toyoshima et al 1985; the inflammation and hyperplasia was more severe than that which occurs in response to ichthyotoxic algae (Chang e t al. 1990); algae that cause asphyxiation were not present in the interlamellar spaces or attached to secondary lamellae (Jones & Rhodes 1994); and there was no excess mucus, oedema, haemorrhage, epithelial cell necrosis, siliceous fragments or foreign body reactions and proliferating epithelium did not retain polygonal morphology as is seen in mortality events due to physical irritation by siliceous diatoms (Ferguson 1989, Yang & Albright 1992, Kent et al 1995. The absence of relevant pathological findings was consistent with the lack of evidence of an environmental insult.…”

“…In scanning electron micrographs there were no adhering algae or algal spines (Yang & Albright 1992) or evidence of mechanical damage in the gills of 2 moribund and 2 dead fish from Bremer Bay, Western Australia. A small copepod was found embedded in the base of the secondary lamellae of one fish; this was confirmed histologically but whole specimens for taxonomic identification were not obtained.…”

Oral l-cysteine ethyl ester (LCEE) reduces amoebic gill disease (AGD) in Atlantic salmon Salmo salar

“…The NAC analogue, L-cysteine ethyl ester (LCEE), was successfully tested as an in-feed additive to protect coho salmon Oncorhynchus kisutch against the harmful phytoplankter Chaetoceros concavicornis (Yang & Albright 1994). C. concavicornis is a harmful marine diatom that irritates the gills of fish leading to excessive mucus production and accumulation, and subsequent mortality (Yang & Albright 1992). LCEE has apparently been tested as an in-feed mucolytic additive for AGD-affected Atlantic salmon without success (as stated by Munday et al 2001), although no experimental design, method, or actual results were given.…”

Three strategic feeding during hatchering of Nile tilapia: effects on organs integrity, parasitism and performance parameters

“…Accumulation of nitrogenous compounds (Rodrigues et al 2012), chemical substances present in water (Roberts 2012) and ectoparasites (Valladão et al 2013) can cause severe alterations in gill structure, compromising the function of its filaments. Lamellar edema is the most common lesion in fish and may progress to necrosis of lamellar epithelium, causing respiratory and osmoregulatory distress, which then leads to a compromise in the health, development and survival of fish (Yang and Albright 1992). Natural feed was more beneficial to health of the gills, which may have correlated to both a low intake of nitrogen compounds in water and a lower intensity of important gill parasites, such as the genera Trichodina, Cryptobia, and Chilodonella.…”