Sublethal effects of a new antifouling candidate on lumpfish (Cyclopterus lumpus L.) and Atlantic cod (Gadus morhua L.) larvae

Abstract

Sublethal effects of medetomidine, a new generation antifouling compound, on lumpfish (Cyclopterus lumpus L.) and cod (Gadus morhua L.) larvae were examined. The effects on respiration rate and on colour adaptation of newly hatched larvae were assessed after 24–96 h exposure. Exposure of lumpfish larvae to the experimental concentrations resulted in a significant decrease in respiration rate (Lowest Observed Effect Concentration (LOEC) = 5–10 nM) and in the percentage of dark larvae (LOEC = 4 nM). However, no effects on respiration rate of cod larvae were detected. In addition to lumpfish larvae being affected at low concentrations of medetomidine, a reversibility of the effects was observed when 96 h-exposed larvae were incubated in clean seawater for 24–48 h. Considerations relating to the future commercialisation of medetomidine for antifouling purposes are discussed.     

Observations on the colours of lumpsuckers, Cyclopterus lumpus L.

Ripe unfertilized eggs derived from fish landed at two Icelandic ports were predominantly red and yellow-red, but a small proportion were red-purple. There was a significant difference between the frequencies of hues of eggs from the two landing places. During the phase of blastula formation, fertilized red-purple eggs showed no discernible change in either hue or chroma. However, as the gastrula formed and covered the yolk, the chroma declined dramatically, although the hue remained unaltered. When the embryo formed, the chroma continued to decrease and the hue also began to change as the red-purple pigment disappeared from the yolk and the orange-yellow oil of the yolk became more visible.
The most common plasma colouration in male fish collected at Hafnarfjordur and Husavik was red, but the observed hues covered 60% of the visible spectrum, ranging from green to purple. No significant differences between Hafnarfjordur and Husavik males in terms of hue or value were discerned, but there was a significant difference in chroma score. Female plasma hues were almost as variable as the males (spanning 45% of the visible spectrum) but centred in the green-yellow zone. Plasma, subcutaneous jelly and skin colours were closely linked.
Fish from the oceanic feeding grounds were all green in skin colour, whatever their age or sex; it is suggested that this colouration has a cryptic function in the near surface waters inhabited by lumpsuckers.     

Short-term movements of larval and juvenile lumpfish, Cyclopterus lumpus L., in tidepools

Larval and juvenile lumpfish, Cyclopterm lumpus L., which attach to marine algae and eelgrass using a ventral sucker, were marked and recaptured in a series of experiments along Schoodic Peninsula, Maine, U.S.A. A repeat-marking experiment in 1988 indicated immigration and, possibly, emigration in tidepools. Yet, some individuals remained in the same tidepool for up to 25 days. Experiments with marked groups of fish in 1988 and 1989 revealed significant short-term residence of individual lumpfish; up to 79% of marked fish were recaptured in the same tidepool 2 days later, even after major storms. A translocated group of 34 lumpfish left the new tidepool within 1 day, but two individuals returned to the home tidepool within 6 days. Extended inhabitance of tidepools by larval and juvenile lumpfish seems to be a function of availability of food and algal cover.     

Further Observations on Cryptobia dahli (Mastigophorea: Kinetoplastida) Parasitizing Marine Fish

Studies were conducted primarily to ascertain the mode of transmission of Cryptobia dahli parasitizing the digestive tract of lumpfish ( Cyclopterus lumpus ). Another flagellate, morphologically similar to C. dahli , was also observed in the gut of a deepsea fish ( Macrourus berglax ). Several invertebrates, which are food for lumpfish, were examined for flagellates, but were neither infected nor showed evidence of cystic stages. Parasites were more abundant in the stomach, especially at about pH 5, than in other areas of the digestive tract. Transmission was achieved by pipetting the parasites into the stomach of uninfected fish, by feeding food contaminated with flagellates, and also by holding infected and uninfected fish in the same aquarium. In nature, lumpfish probably acquire parasites during winter when they aggregate and regurgitate into seawater because parasites can survive for short periods outside their host.     

First record of Cyclopterus lumpus L., 1758 (Osteichthyes: Cyclopteridae) in the Mediterranean Sea

The Atlantic lumpsucker Cyclopterus lumpus (343 mm total length) is recorded for the first time from the Mediterranean Sea. The specimen was collected in the night between 16 and 17 September 2004 off Molunat Bay, Croatia, southern Adriatic Sea. This record may present a case of a vagrant specimen.     

Observations on skin colour changes in juvenile lumpsuckers

This study reports on an experimental investigation of colour change in young lumpsuckers Cyclopterus lumpus , employing Munsell colour charts to quantify skin hue, colour value and chroma. Juvenile lumpsuckers can live pelagically close to the sea surface, or can attach to floating seaweed and debris with their suckers. When swimming they adopt a cryptic default light green coloration, with the dorsum being darker than the belly (countershading). This default colour is also seen in complete darkness. When attached to objects they take a colour stimulus from below and to the sides and change colour. They can achieve good colour matches (noticeable in 3 min; complete within 15 min) with substrata that are green-yellow in colour, especially the brown alga Ascophyllum nodosum . Colour matching is largely dependent upon changes in colour value (i.e. lightness/darkness) produced by melanin dispersal or concentration in the melanophores. Thus, on artificial backgrounds outside the range of achievable hue matching, they still achieve good matchings of colour value. Slight hue changes were recorded (probably reflecting interaction of basic skin colour with melanin dispersal state), but chroma (brightness) variations were negligible. Lumpsucker colour depends upon light intensity, allowing sustained colour matching as weed illumination changes.