Life-history strategies of pike in a high-altitude loch in Scotland

Pike, Esox lucius, are present in Loch Callater at their highest altitude and most extreme habitat in the British Isles, with subarctic winter conditions and extended winter ice-cover. The response of pike in this environment is slower growth, due to a shorter growing season and the low availability of forage fish, giving the poorest reported length-at-age for pike in the British Isles. All pike were mature or had spawned in the same year, with gravid ovaries in April and normal recovering ovaries in June-July. As in other lochs with few prey fishes, the larger pike ate small items such as invertebrates

Life-history strategies of pike in a high-altitude Loch in Scotland

The pike, Esox lucius, a top piscivore of fish communities in north temperatefresh waters (Raat 1988; Craig 1996), is common in many lowland waters inthe British Isles and is normally found in diverse fish assemblages which mayinclude cyprinids, percids and salmonids. However, in Scotland where fishspecies diversity is restricted following the last glaciation, ca. 10,000 years ago(Maitland 1977), the pike is mainly found in simple fish assemblages and maybecome the dominant species by suppressing salmonid stocks. The pike is alsoa major predator of duck chicks and can restrict the distribution of certainspecies of waterfowl in highland lochs (R. N. Campbell, personalcommunication; Treasurer 1980; Maitland & Campbell 1992). In northern andeastern Scotland, pike are frequently present in simple predator-preyassociations with perch (Treasurer et al. 1992). In these lochs, pike numbers(5.4 per ha), biomass (range 3.9-5.9 kg per ha) and growth rate are typical ofpike in other waters in the British Isles (cf. Raat 1988)

Inhibition of sexual maturation in tank reared haddock (Melanogrammus aeglefinus) through the use of constant light photoperiods

The haddock (Melanogrammus aeglefinus) is believed to be a potential candidate for aquaculture in the Atlantic coastal countries including the UK, Norway and Canada. However, under culture conditions, haddock will sexually mature prior to the attainment of a suitable harvest weight. Therefore, a long term tank based experiment was performed where three populations of haddock (hatched spring 2002, approximately 150 fish per population) were exposed to either a simulated natural photoperiod (SNP) or SNP until January or July 2003 and thereafter continuous illumination (Jan LL or July LL respectively) with individual growth rate and maturation status being recorded until July 2004 (27 months post-hatch). While the SNP treated population matured in the spring of 2004 (two years post-hatch) with 88% of the population being observed to release gametes, no mature individuals were observed in either of the LL treated populations and furthermore there was no evidence of gonadal development or elevation in sex steroids (testosterone, estradiol- 17 beta or calcium). The application of LL appeared to directly stimulate the growth rate of haddock (e.g. 14 to 27% increase in weight thermal growth coefficient) and improve food conversion rates. At the end of the trial there was an approximate 50% increase in wet weight (SNP: 647 +/- 53 g, Jan LL: 982 +/- 34 g and July LL 985 +/- 33 g), however no significant difference in weight in relation to the length of LL exposure was observed. Plasma melatonin analysis revealed that the natural diel rhythm had been inhibited in both LL treated populations. Along with highlighting the similarity in reproductive entrainment between haddock and other gadoids, these results demonstrate how photoperiod manipulation could be used as a management strategy to improve growth performanance in farmed haddock stocks. (c) 2007 Elsevier B.V. All rights reserve

A review of the impact of parasitic copepods on marine aquaculture

In recent decades, aquaculture has become an increasingly important part of the world economy. Other than marketing concerns, the biggest challenge facing fish farmers is to control the many complex abiotic and biotic factors that influence the success of fish rearing. An example of the complexity involved in managing aquatic systems is the need to control opepod populations by manipulating the pond environment. Copepods play major roles in pond ecosystems, serving as 1) food for small fish, 2) micropredators of fish and other organisms, 3) fish parasites, 4) intermediate hosts of fish parasites, and 5) hosts and vectors of human diseases. Planktonic animals, especially rotifers, cladocerans, and copepods of the order Cyclopoida are the most important food items in freshwater aquaculture, and copepod nauplii are especially valuable for feeding fry. Copepods used as natural food are either cultured or collected from natural water bodies. Adult and advanced copepodid stages of cyclopoids are micropredators that target early life stages of cyprinids (Cyprinidae). Other copepods in aquaculture are fish parasites. The most common adult copepod parasites of freshwater fishes are Lernaea cyprinacea, Ergasilus sieboldi (and related species), Salmincola californiensis, S. edwardsii, Achtheres percarum, Tracheliastes maculatus, and Caligus lacustris. In addition, copepodids of Lernaea and chalimus larvae of Achtheres and Salmincola attach to gill filaments and cause epithelial hyperplasia and may be indirectly responsible for fish-kills. Copepods are also intermediate hosts for important fish parasites, including tapeworms and nematodes. Damage from these parasites may lead to fish mortalities or reduce the market value of the fish products. Finally, copepods serve as intermediate hosts for parasites that infect humans and can serve as vectors of serious human diseases like cholera.Peer reviewed: YesNRC publication: Ye

Effects of Fish Meal Replacement with Full-Fat Soy Meal on Growth and Tissue Fatty Acid Composition in Atlantic Cod (Gadus morhua)

Atlantic cod of initial mean weight ~220g were fed a control diet and three diets where fish meal (FM) was replaced with increasing levels of full fat soybean meal (FFS) supplied at 12, 24 and 36% of dry diet, for 12 weeks. There were no significant differences in final weights but the specific growth rate (SGR) was significantly higher in fish fed the control (FFS0) diet compared to fish fed the FFS12 and FFS36 diets and the feed conversion ratio (FCR) was significantly lower in fish fed the FFS0 diet compared to the other three treatments. The fatty acid (FA) compositions of the cod muscle and liver were highly affected by dietary treatment and linear relationships between dietary and tissue FA concentrations were shown for some of these. Moreover, selective utilization or accumulation in the tissues of specific FA was suggested by the results