Evaluating effects of water withdrawals and impoundments on fish assemblages in southern New England streams,USA

Abstract Balancing aquatic conservation and water supply is becoming a major global issue for urban landscapes. The purpose of this study was to evaluate the ecological effects of stream‐flow alterations via water withdrawals and impoundments on fish assemblage structure. Electric fishing data were collected at 33 wadeable streams in Connecticut, located in the Southern New England region of USA. Fish sampling was conducted directly downstream of water withdrawals for municipal and agricultural water supply, and study sites differed in potential water withdrawal rates and the presence of impoundments. Regression analysis showed that water withdrawal rate was more important than other natural and anthropogenic factors (e.g. landcover and stream size) in explaining several fish assemblage metrics. Stream sites with high withdrawal rates were generally characterised by lower proportions of fluvial dependent fishes (fish which need flowing water to complete a portion of their life history) and benthic invertivores (fish which feed on bottom‐dwelling stream insects in riffle habitat), and had a greater percent composition of macrohabitat generalists, particularly members of the family Centrarchidae. Some assemblage metrics responded linearly with increasing magnitude of water withdrawals, but others were non‐linear. Results are consistent with ecological theory that alteration of the natural flow regime will impact stream biota.     

Effect of ethanol, clofibric acid and temperature on the uptake and elimination of 2-methylisoborneol in channel catfish (Ictalurus punctatus)

Off-flavor, due to organoleptic compounds such as 2-methylisoborneol (MIB), is the single largest detriment to the harvest, production and profit from the channel catfish aquaculture industry of the Southeastern United States. Methods to increase the metabolism and/or elimination of compounds like MIB would provide a means towards improving catfish rearing practices. Previous studies indicated one or more forms of cytochrome P450 monooxygenase (CYP) may be involved in the biotransformation and elimination of specific organoleptic compounds, such as 2-methylisoborneol (MIB). In order to determine the role of CYP in the elimination of MIB, various compounds that have been shown to modulate cytochrome P450 expression in catfish were administered before and after exposure to ¹⁴C-MIB. Uptake and elimination was monitored in fish over 24 and 48 h, respectively. Pretreatment with clofibric acid (100 mg kg^–1-gavage) which induces a CYP2K-like isoform, and ethanol (1.0% v/v-aqueous) a CYP2 represser, alone and with enhanced temperature (added 10 °C) failed to affect uptake of MIB. Pretreatment with these compounds and conditions also failed to enhance elimination of MIB from channel catfish. However, when fish were treated with 1.0% ethanol after MIB exposure (i.e., during depuration), beta elimination halflives were changed from 144±35 to 71±13 h. in sexually mature animals but unchanged (191±113) in juveniles. The failure of CYP-modulating agents to alter MIB elimination in catfish suggests MIB may not readily undergo Phase I oxidation via CYP. The enhanced elimination of MIB in adults by ethanol warrants further study as to its potential use in aquaculture in purging MIB and related compounds prior to fish processing.     

Effect of fish feed processing conditions on digestive protease activities, free amino acid pools, feed conversion efficiency and growth in Atlantic salmon (Salmo salar L.)

The responses of the digestive proteases trypsin and chymotrypsin and protein metabolism to differences in feed protein quality were investigated in Atlantic salmon (Salmo salar L.). Two sets of experimental feeds were produced. Each set of high and low quality feeds was provided to either 150 g or 2 kg salmon. Protein in the high quality feeds had significantly higher percentages of free (reactive) sulphydryl (SH) groups than the corresponding feeds based on low quality meals. After 90 days feeding, groups given high and low quality feeds did not differ in their specific growth rates (SGR) in either experiment. However, feed conversion efficiency (FCE) was significantly different between the high and low quality feed groups in 2 kg salmon, where the difference between the high and low feed protein qualities was larger, 10% versus 4% SH/[SH + (S–S)] in 150 g salmon. Higher FCE was preceded by significantly higher trypsin and chymotrypsin specific activities on day 60. SGR, in general, changed after the first month and was stable during the last 2 months in both experiments. Concurrently, both trypsin (T) and chymotrypsin (C) decreased with an increased activity ratio of trypsin to chymotrypsin (T/C ratio), and resulting in significantly lower T/C ratio on day 90 in salmon feeding on high quality feeds in both sizes of fish. Differences in FCE were associated with significant differences in levels of total free amino acids (TFAA) in the plasma and the white muscle, as well as in the ratio of essential to non‐essential free amino acids (EAA/NEAA ratio), free hydroxyproline, and RNA in the white muscle. Interestingly, after 3 days starvation (day 93), 5–7 h postprandial EAA/NEAA ratio in the plasma was significantly lower in the high quality diet groups in both experiments. Trypsin specific activity inversely correlated with muscle TFAA levels in 2 kg salmon, concurrent with higher muscle levels of RNA, lower free hydroxyproline and higher FCE in fish fed higher quality diets.